Mother won't be logical. How do I handle the situation and do what is best for us all?

Mother lives in annex attached to our house - built two and a half years ago for the purpose because she wouldn't do it before. She is 90.
She has severe rectal prolapse causing constant pain (although she won't take pain killers so I am not sure of level) or certainly discomfort, and is doubly incontinent. She is waiting for a consultant appointment (colorectal) to see if they will do a colostomy so they can remove the prolapse - although chance of this is probably one in 10 as she has COPD. Dr tells her she is fully capable of living independently and colostomy will make life so much better, but raises false hopes in my opinion as he has not discussed factors which will effect whether she can have Op or what she will have to cope with after. (Leakage due to difficulty of application and frail skin could well lead to as much pain as she has now, and physical changing of bags will be difficult due to reduced hand movement etc. She requires what I can only term superficial social interaction- before she moved in with us neighbours popped in half a dozen times a day, we live in the country and apart from us she sees maybe two people a week for an afternoon of bridge, and a coffee morning if she is feeling well enough. However she is obviously missing the social interaction and complains of loneliness all the time. She also complains of being despondent or depressed because she doesn't see where her life is going. We expected when she moved in that odd nights away to see the family (which cannot be done in one day) would be OK, but she refuses to be left alone for even the one night so we are unable to go and see our children. We took a holiday last year for three weeks with the plan she would go into a retirement home for the period which we thought would give her a chance to try it out - however she arranged to stay with 7 different friends instead, and to get bus with her cases etc. Luckily we managed to get this altered to just her cousin (93) and a friends daughter. We have help for her to have a shower once a week but she has been assessed as needing no care. However she neither cooks regularly nor eats food I provide for her. A lot of days she decides not to get dressed - "no point, I'm not seeing anyone". When she does see someone other than us she is bright and cheerful, very sociable, although it leaves her tired and she may sleep all the rest of the day. When she sees us she is what can only be described as whining and with a pathetic act. We have no lives, as she makes such a fuss if left at all, and we want to have some retirement before spinal and arthritic problems I have stop us being able to do anything. What can anyone suggest we do - I know I sound sorry for myself and whineing (my husband is much better with her )- unfortunately she created a very bad childhood environment which means we really don't have a relationship, in fact I actively dislike her which makes having an annex built even more stupid. She causes me anxiety and the current position is causing severe depression and even thoughts of suicide which I had got past for the past 20 years. How do I handle the situation and do what is best for us all? I should say that whilst she is alert most days, and knows what is happening, she has poor short term memory and little ability to reason. There is no signs of actual dementia (according to Dr) and no family history of it.