How can I protect my mother's personal items/memorabilia from being given away/sold/thrown out?

I think, because the relationship is rocky, you might be out of luck.
But still, there are a couple of approaches that *might* work --

Straightforward: "Sis, I've been thinking about a few sentimental things of mom's: Gr'ma's sewing basket, Gr'pa's woodworking set, what ever . . . .and thought it might be nice to have them if you were not planning to keep them" Sort of thing.

And you can play that two ways -- one, asking for the things you truly do want, or two, asking for things you don't care so much about .. . . to test her and see what she does (Oh, that old thing, I already donated it to Goodwill, . . . . or she disposes of it after learning you wanted it -- depends on how mean she is and this will test that and let you know :)

Or sneaky: You could wait until your next visit and go the route of "Gosh, sis this sorting through stuff is going to be overwhelming, let's get started on it while I'm here" and promptly "Sort" the things you care about first . . . right into your vehicle.

I'm assuming all this parting with things would be ok with your mom though.

Also, if any of these plans get your sister riled up and she throws out a "Just take it all then if you want" type of temper tantrum . . . jump on it before she cools off and DO take the items that are important to you. She'll change her mind, and maybe get rid of them once she cools off. That is the only way my sister and I have possession of my Great Gr'ma's quilts and several other sentimental items of my dads -- turning an temper tantrum ultimatum to our own good use ;)

Best of luck, I'm the sentimental one in the family, so I really feel your heart on this {{{hugs}}}

Sorry the relationship is rocky. Sounds as tho your Mom lives with this sister? She is then doing her best. I think you should simply offer support. Visit. Ask Mom if she would like to make a scrapbook with you? Try to get some memories that way. When my Mom died I sent all the albums they had in the mail. ALL WERE LOST save the few I tucked in a book and took home myself, including a wonderful wonderful album my Mom had made for my Dad of his old girlfriends! That one hurt the most. I would go through them saying "Dad, you are lucky you didn't marry HER". In any case, my heart was broken. But my partner was right when he told me "Al, you will look at those twice more in your life, and then pass them down, and NO ONE WILL CARE". He is right. We are leaves on the tree. I think this when I go to junk sales which I love, and find entire families left to the vagaries of fate. THE TIME IS NOW. You have a living Mom and a living SISTER. (unless I missed it and your Mom already passed). Give them love and honor now. Appreciate their beauty (and all the other stuff too) now. If indeed your Mom is gone, then ask your sister with love, if she could share with you some of the memories. If she is angry and unable, let it go, and move on.

I think the best course of action it to try to mend your relationship with your sister even if it means being the bigger person. POA doesn’t give you the right to go in to her house and take things (I am not saying you would try to do that). In order to take legal action you would have to prove what belongings she has. So really I think the best thing you can do is try to let bygones be bygones & try to fix the relationship with your sister and get to a place where you can discuss your mother’s belongings and when to go through everything together. Even if your sister is the bad guy here, prepare to be the bigger person. Good luck!

Good luck but situations like this are usually a hopeless case. Unfortunately, your sister holds the cards and she doesn’t sound like someone that you will be able to reason with. I’m so sorry that you have to deal with this. Many of us have siblings that are rotten to the core.

Sending a bazillion hugs your way! 💗

It depends on the people involved. If your sister is spiteful you may have to resign yourself to not getting them. If your mom is capable have her write a list and give it to her or maybe she’ll let you take them now. My mother gave my cousin stuff I particularly asked if I could have, like my grandmothers bed , because she had an “old house” and “it fit better there” ( When I asked, she acted happy I wanted them and my house is well over 100 years old , older than my cousin’s lol) . I just chalk it up to her narcissistic and abusive personality and moved on. You can’t worry about stuff you have no control over.

FloridaCare1958, I am so sorry to read your post and I truly understand your concern(s).
1. Do you have any siblings?
2. Have any items magically disappeared?
3. Does Mom have a Will? If so, have it recorded with the County Recorder's office. Not every State allows this, but you can make the argument as POA. This is important if your State is Probate. This will also help your argument should a 'new' Will be presented by a sibling; this will then become an issue of fraud or advantage of an elderly person.
4. Call the insurance company to ask about whether or not ALL of the contents of the home are insured. Ask for a recommendation for a company to video everything in the house. This will serve many issues that could pop up.
5. This will cost a bit, I had to pay $500 for a basic service from an Estate evaluation company to come into my Mother's home to take pictures, determine hers/his/theirs (I have ugly step-siblings who are EXTREMELY GREEDY). The company will place on CD as well as provide you with a catalog of everything with the listed value and the total value of the estate. If you have an attorney make sure she/he receives a copy too. Give copies of ALL LEGAL documents for attorney's file regarding your position of the POA.
6. As POA, you do have the right to take ANYTHING OF VALUE from the home ONLY AFTER INFORMING ATTORNEY AND PROVIDING PICTURES OF THE ITEMS, BUT you must place it all in a safety deposit box for Estate settlement. This will also protect property if you have in-home care as well as proving YOU didn't take it for yourself. My Mother had some very expensive jewelry and heirlooms which are no longer around. I do not have any idea who either talked Mom into giving a piece to them or if someone in the family (including step-children) went through her jewelry box and stole pieces.
7. Constantly check the County Recorder's website for ANY DOCUMENTS FILED. You should be able to print ALL documents and attachments. This will help should someone talk Mom into signing legal documents should she be suffering from dementia etc. Persons with any mental issues cannot sign a legal/binding document.
8. Become Guardian so no one in your family can question your acts to protect unless they take you to Court. Talk with your attorney about this.

I am Mom's Guardian as well as living out of State. I have a Court order which allows me to keep every family member from entering the house since I had to place Mom in assisted living. I changed all the locks, pissed off ugly step-sister and I only gave a key to Mom's 2 brothers for emergencies. Ugly step-sister is now forced to 'settle' monetarily as I am getting a protective asset divorce for Mom. Ugly step-sister will have to accept MY demands or at least 99.9% especially as I have several State/Federal illegal actions she did. The State is 50%-50% marital debt or Community property and she owes Mom's Estate just under $90.000 now.
Cover every single scenario you may encounter. It may not be something to worry but just like questions, there isn't a stupid questionable situation. Make sure your attorney provides you with Federal/State statutes in laymen verbiage. I have 3 ring binders full.

FYI: REVIEW THE SECRETARY OF STATE RULES/REGULATIONS FOR NOTARY. THESE CAN BE REVISED AND 99.9% OF NOTARIES DO NOT READ THE REVISIONS.
If I had not done this I would not have ever caught the change of beneficiary deed my older sister had Mom sign! THE NOTARY DID NOT COMPLY WITH THE NEW REVISIONS.
My attorney wasn't aware of some very important changes until I pointed them out to her and she is a notary. Print a copy and place it in a binder so you are able to have immediately at your fingertips.

Thanks for all the advice. My mother lives in a residential home for dementia patients a few miles from my home, I am her caregiver in addition to the staff there. My sister lives in another state. I reached out to her to inquire as to what things she has from Mom's house (she handled the sale and assured my mother that she would save all of the "important things" for her). She refused to let me know what she has. I do know that she has all of my mother's photos. That is really the only thing I care about. I have no pictures of me, my family, my parents when I was growing up, my mother saved them all. Therefore it would be heartbreaking if these pictures were destroyed. I've enlisted the assistance of my daughter who will reach out to her Aunt and ask for the photos. Hoping she's successful. Again thanks for all the advice. I'm still in shock that this relationship has become so toxic.
New Year, New attitude...….avoid the drama.

I would want the pictures for Mom. Looking at them may bring her some joy. I love to look at pictures even if I don't know everyone in them.

Maybe sister can scan and email.

There isn't necessarily anything of any cash value at all - the items I've kept that belonged to my mother are mainly photographs and books, and the lost item that I'm most annoyed about is her address book. Which my sister took immediately after her death, volunteering to notify mother's friends and former work colleagues, and then tossed. Adding insult to injury by claiming that she'd asked me if I wanted it. And further insult over many months after mother's death and her funeral from the number of people who expressed their hurt at not having been informed.

Now I'm sorry I started answering...

Sigh. FloridaCare, one thing you perhaps can do is use your mother's money and your POA to hire a storage unit and pay a removals team to clear your mother's possessions out of your sister's house under your sister's supervision. Might she co-operate with that?

My mother has nothing of 'value' and few things I would consider to even have sentimental value. She has, over the years, promised many of her 'valuable' things to several people. She puts sticky notes on the bottom of the item and there will probably already be 2 or 3 names on this already.

She's 'promised' me the bedroom set that was my Grandma's and the only thing I would even care about having. Just heard that when she passes the oldest daughter of the 'house' (Mom lives with YB and his family) will inherit these lovely pieces of furniture. I'm glad I found out, in a roundabout way about this switcheroo. Not that is makes any difference to me, really, I am just glad I won't have to be hurt and surprised at the time.

No 'thing' is worth the grief that can be caused by an elder forgetting to whom they have 'promised' stuff and how it can literally break up families for good.