She pooped on the carpet

I don't know what to do. A cat that pees and poops on the carpet can't live in a house with a baby. But we've kept her with us through kidney failure, and she's doing so well on a health-related basis. And the vet says there's nothing medically wrong with her that's causing this, so we can't treat her and try to fix it.

Her box is clean. She should be using it.

I don't know why she's refusing to use her litter box. But we're starting to run out of options now, and it makes me sad. I don't want to do what I suspect we may have to do. But I don't know what else to do.

I love her.