Around 5 years ago my family moved into my grandmothers house shortly after my grandfathers passing, ever since my parents sold our home and moved in it's like she despises us (me, my sister, mum and dad) to begin with she would just be silent and make arguments out of nowhere, would moan about the mess of the house (even though my mother cleans it every day after she comes home from work) would say we don't want to do anything for her when that's what we moved in for and calls on other members of my family (cousins, uncles etc) to take her places when we could have easily taken her. Now 5 years down the line things still aren't any better she has been diagnosed with depression and diabetes of which we know by finding out from other family members because she doesn't tell us anything, I only work part time so I'm in the house the most and hear her anger outbursts a lot, she mostly takes it out on our dog by screaming at him, she used to throw things around the house but no longer has the strength to do so, she leaves the stove on constantly and always leaves our front door open. What is worrying though is that she just seems to be like this around us and it's like a different person when anyone else enters the house?! I'm just wondering if there could be signs of anything like bi-polar or dementia? I'm not familiar with anything like this I just don't know anyone else's grandmother that acts like this.
It could be a number of things such as infection, mental illness, dementia or something else.
You say that she is secretive about her medical conditions. She could have been told that she has other conditions, but is not telling you. Will she allow you to attend doctor visits with her? Are you her Healthcare Power of Attorney? If not, then it may be difficult to have her examined and evaluated. Is there any other family member or friend that she would trust to see the doctor with her. You can also send her doctor a letter describing your concerns. He may not be able to give you info, but you could provide it to him.
It certainly sounds like her behavior should be discussed with her doctor. If she is in the earlier stages of dementia, your input can help the doctor see what may be going on. In the early stages of dementia, if that is what she has, the patient may often appear normal before some people and then appear problematic later at home. I've read on this site that it is called "showboating." The patient can hide parts of the illness, but for a short time. Eventually, they won't be able to do that and the memory loss and bizarre behavior becomes more obvious.
Try to protect the dog and any children that may be in the house. If it is dementia, she may not be herself. It's a rough road to help protect a family member who is not open to help, but it can be done. I would first determine what is causing her behavior, research how to help her and then make plans regarding your family. If that is not your house, you may have to figure out how things will work out regarding her long term care.
This site is a great place to come for tips and support.
Why would she go out of her way to arrange a ride from someone outside the house when the 3 of you are right there and willing to take her? Is she telling people that you and your family don't take good care of her?
If you're concerned about her recent behavior take her to the Dr. for a check-up. Maybe one of her medications could be causing this behavior.