I don't know the exact stage she has, but it may be stage 6. Not stage 7. It depends on how the caregiving goes. My FIL who has stage 6/7 AD has had the same problems over the years.
First of all, regarding eating, does she choke a lot on the food or water? If she is in late stage, she will have trouble swallowing. My FIL has had this problem for 2 years so now he is having pureed food to prevent him from stopping eating completely.
You need to puree the food so she can swallow. She would not understand what to do with the food. Also, my FIL stopped knowing about food and getting cakes in the kitchen last year, so your Mom may also have stopped knowing that she needs to eat. People have to cue them. My FIL has moved to this residential home last summer and they cue him and take him to the cafe to eat with other residents. He is quite happy with that.
So try some babyfood and pureed food. Also, don't push her to drink. At this point, she could cough and get aspiration pneumonia. So watch out for that. If you feed her something that will choke her or make her cough, she will refuse it.
Secondly, it is tricky about walking. My FIL lost his balance on walking in late 2007. He had managed to walk with a cane since then until this May. Now he can no longer walk on his own and the walker is not that useful - he can no longer gets up by himself and all that. In 6 months, he may need wheelchair and become chairbound.
You need to find out from the doctor what level she is walking. If she needs a cane, get it for her, if she needs helps, be there.
Walking next to her can help her balance.
Now my FIL can only walk a room's distance on the walker poorly and gets very tired and wants to sit down. If she is at this stage, don't push her to walk. Get a wheelchair so you can transport her. Get her up every 2 or 3 hours.
The thing is you cannot just make her do it without understanding the tricks with dementia.
They cannot be pushed or forced. You have to be nice to her even if she is mean. You may need to say white lies to her.
It would help if you hire a home care nurse or someone who can manage the elderly's dementia and she/he can tell you what to do with her.
We hired a home care co. nurse back home and she had helped a lot. Also read some books on Alzheimer's to understand how she thinks.
Your Dad gets hit by her a lot partly due to his demand on her.
Don't demand her to do things, persuade her, babytalk her... It is hard, but it is the only way. If you get upset, she gets more upset and will fight endlessly...
There are many other stuff you need to know. She is afraid of water, so don't make her take a shower on her own. Be there in the bath, draw the water for her to tell her the temp. is OK and etc. Sponge bath may help. She needs to be told to wash her hands. Her brain has been damaged so don't think she can do it on her own anymore.
If she is frustrated with everything you did, she may just want to tune out and sleep on her own. It could also be that she is in late stage closer to stage 7 like my FIL. Your Dad and the family need to change the way of approaching her. She does not understand it is "your help", so work on it from her perspective.