help for a friend

I care three times a week for elderly woman who is mother to close friend. although early stages we shop shop shop i pick her up and drive her wherever she wants to go. we eat then shop she is allowed $60 a day and inevitably goes over forcing me to dig in my pockets which i do willing she is kind then mean and discusses her daughter with such disgust it hurts me she is just so horrid to her who lives with her and between her brother alternates taking care of her after work in to the evening every day she is taken to lunch and dinner every day but there is only so much i can say bc she becomes difficult and argues she constantly says her husband left her a boat load of money which he did not and she should have it rather than being treated like a child that she should have a CC and ability to spend what she wants,, i remind her money has been transferred twds later care and that if it wasnt dispersed this way she would go through it too fast she remembers all this but i am kind to her and she really does love me and remembers so many things its hard to know when the disease is affecting or not but i find this discussing her daughter is so hurtful i witness daily the horrid way she discusses her and finding fault with her at every step is this the part of reasoning that has affected her so? is it always the disease? her sons advise friend that she must remember this is not the same woman she grew up with but it is hard i am unsure how to help my friend i found this site very insightful and helpful but couldnt find answers to our issue IE; is it always the disease doesnt she have lucid moments of clarity? why is her anger directed towards a loving family member making care taking difficult? she claims she will never go into assisted living she will die first and i am not sure how much longer i will be needed as she becomes increasingly difficult becoming angry with even me over trivial matters ive become afraid i might lose her in store but she likes to shop alone soemthing her daughter wont let her do i dont argue but rather change the subject she is constantly purchasing items then returning them so she can have cash if she does this dosent she have clarity and then the return for money require sophisticated thinking but the becoming instantly insulting twds me is this all the disease her constant insults twds daughter is hurtful and sad very sad trying to remind her how mush she is loved only angers her at times other times she listens and is quiet please respond appreciate any advice