Roles in caregiving too much or too little?

My significant other of 27 years, a 68 year old only son, is his 91 year old mother’s only care giver as she lives next door to us on his farm and her home is fitted with rails and handles. She is fiercely independent and other than paying a younger male friend to drive her into and around town (20 miles one way) she does yard work around her rentals, takes care of her various business rental related details, and has lunch at the Senior Resource Center four or five days a week. I send meals over most nights because she still prepares her own breakfasts and some lunches and a few times a month she, son and I eat out. About two years ago she had a heart valve replacement after a heart doctor she had less than 2 years to live, followed by two knee replacements. She’s had a great recovery except she says she feels dizzy a few days of the week and after getting her medications changed several times she doesn’t take anything but a baby aspirin and 25mg of Metoprolol Succ 1x day. She takes her blood pressure 5 or 6 times a day and if it’s high - 180/90 or higher she takes a hot shower or works in the yard and it comes down and lately reports that it's normal. She failed to get a recommended MRI for her head before her operations because she thought the surgeons might not operate on her, She has had at least 3 TIAs over a period of about three years. I was with her for one TIA, she said she couldn't get the right words out (she did but not in the right order but I didn't know what was wrong, looked it up on the internet when we got home and told son about it) and another - she says she “fell asleep” at a stop sign on a nearby rural road and the car she was driving rolled into a tree which bruised her up a bit - she quit driving after that - and now she acknowledges she had another TIA a couple of months ago while talking on her cell phone at home but still refuses to see a doctor. Her heart doctor put her on a blood thinner which she refused. He also says to keep as active as she can and she does several hours of gardening nearly every day with several breaks. For about 20 years she was an x-ray tech and feels she knows more about her body than her doctors – and sometimes shes right. But she says using a cane makes her look old. The worst case scenario happened two days ago; she called and said she was "in the emergency room and she had fallen but the doctor just came in" so she hung up. We were frantic for about 15 minutes and she called back saying she was actually in urgent care and had just been released. The full story came out later that she tripped over the SRC parking lot curb on her way to lunch and fell onto her knee and hip and used her arm to break her fall but still hit her ribs on the curb but insisted on going to lunch! Later because of pain she thought she dislocated her shoulder she went to urgent care and got an x-ray, nothing broken or dislocated, they bandaged her scrapes and let her go. She went back to her rental and gardened some more! Two days later she’s really hurting, says a doctor or taking any oc pain medication is useless and thinks she may have internal bleeding because something may have “torn loose” in her chest and son is about run ragged because of all his commitments. I’m 70 and because of my health limitations can’t lift her up so she can get out of bed for the bathroom. Son is getting a lift recliner today so she can lay in it and get up with no pain. So it's a wait and see situation I guess, in the meantime anxiety over her well being is always there. It’s so hard to know how and if or when to exercise some control over her or do we just let her hurt herself; she seems quite lucid 99% of the time but then we aren't with her 24 hours a day. We don’t want to hurt her feelings and un-empower her but this is getting scary and I am in no position to do anything but offer advice which she doesn’t want to hear. I told son at the very least to get her in for an eye appointment to rule out any peripheral vision problems when/if she recovers from this because another fall may be her last and to order her to use her cane or walker.
PS. Health insurance and money are not a problem but she hates to spend it on herself. One big problem is lack of adequate health care providers in this small town with severe economic problems. One reason she and son are reluctant to get an outside caregiver is that she is a hoarder and he has those tendencies too and they don't want interference with their "problem". I have a hard time watching this all unfold with no ability to do anything except hope for the best, is this normal?