How do I continue to cope with caring for mother (89) who constantly complains and refuses to go into an assisted living?

I am 64 years old and having been living with her for seven years after my husband passed away and left me in debt. She doesn't drive but expects me to get her out at least three times a week even though she is on a walker and can barely stand for five minutes without having to sit down. She is able to do little things around the house but refuses to because she thinks she is the center of the universe and everyone, especially me should cater to her every whim. I have brought up the subject of an Assisted Living arrangement which would certainly give me my life back and mentioned she would have other people her age to talk to. Her answer to that was " The only way I'm leaving this house is in a body bag!!" How do you react to that??? I am so stressed, depressed, angry and cannot sleep through the night anymore because of her constant nagging the demands she puts on me.