Alzheimers\Dementia loss of movement

My 83 year old Mom has been having symptoms for a couple of years but they began to escalate about a year ago at a rapid rate. She absolutely refuses to admit she has a problem and has refused all diagnosis. Her primary care physician thinks it is one of the rapidly progressing types of alzheimers but we can't be sure. He has also watched her become very abusive to me even in his office and has expressed his concern about my being a domestic abuse victim from her. About last October she began to lose the ability to walk and we tried a rehab facility for three months but she refused to participate in any OT or PT. Her mobility rapidly declined and now for the last three months she has been completely bed bound and incontinent. Interestingly when she first became bedbound and refused to even attempt to walk I would see her on camera getting up to get things out of her mini fridge at night and walking independently. But even that stopped after about two weeks or so. At this point she can't even roll over independently. She seems to enjoy being taken care of completely and waited on. I needed a bit of respit and my sibling came in for three days for the first time in over a year (I am her sole caretaker other than hospice) and my sister started really catering to her every whim more than I do and feeding her like a baby. Now since my sister left my mom won't even attempt to feed herself. Before my sister came she was feeding herself with finger foods. Now she wants to be fed and won't even drink on her own. I feel like we need to make her keep what little independence she has (such as feeding herself) and my sister gets mad at me and says I should help her more. My mom often doesn't know who I am and has delusions about her daily activities and people - for instance she thinks my dog is a "man with a mustache" that she doesn't like and she talks about going places which never happens. She is very angry and abusive to me much of the time. I am exhausted by her and really getting burned out. It was emotionally very hard for me to handle her refusing to get up at all even to transfer to a bedside commode and then seeing her walk independantly across the room in the middle of the night to get a soda. She is not a small woman so her care is very physically and mentally demanding. She can still verbally communicate very well, if much of what she communicates is nonsense. At any rate this is a very frustrating journey and I feel so alone and embarrassed about my feelings of resentment.