How to handle a difficult mother who refuses to go to assisted living?

My mother, who has dementia, has in home aides a couple of hours a day. They are supposed to help her bathe, take medication, do light housekeeping, and drive her to her many social activities. (She has a LTC policy that pays for this.) Unfortunately, the home care aides do what she tells them to do , and not what I have told them to do, which means my mother seldom gets a bath, and that she forgets to take her pills without a reminder. I want her to move to assisted living, and I put deposits on two different facilities. Her doctor says she MUST move to assisted living or get 24 hour a day in home care (based on recent cognitive testing). She laughs in his face! I am thinking of starting the legal process to get a guardianship, but I have no support from my sister who says our mother is happy (living in squalor -- did I say she refuses to have her house cleaned?). Her friends are calling us with concerns. She is showing up to bridge in soiled clothes with holes and serving moldy food to guests. She put back in the refrigerator old food an aide had thrown in the garbage. My mother says if we go the legal route she will never speak to us. Advice please!