Cat incontinence problems?

Hello, I have a 5 year old cat who is paralyzed in her back legs. she just drags her hind parts around. needless to say she does not use the box as she does not know when she is going potty. I have let her roam free and do her business wherever for years. i had to steam clean my carpet at least every month, and when i moved into my new place, i started putting her in diapers. i was thrilled they stayed on, but this caused another problem. she got a bacterial infection, got diarrhea, so i had her on antibodies and took her out of the diapers. ever since she has been out of the diapers, she has had poopy problems. she gets constipated then she gets diarrhea with some firm stool mixed in. she wont go for a couple of days, then when it does come out, its all juicy before the normal poo comes out. I have been on my hands and knees cleaning poop spots for two months now, i have spent so much money at the vet that i can not afford to take her anymore, and i feel horrible for causing all these problems, i am at the end of my rapidly fraying rope. i cook oven roasted chicken for her to eat, she does not seem to feel sick and eats and drinks a lot. Does anyone have any idea what i can do to get her regular again?