I am so, so very sorry, my dear friend, @Ltryptophan. You could get a second opinion on your cat’s medical condition, and just for your own peace of mind, and if you can afford it, you might want to go ahead and do that, just so you know that you did everything within your power and financial ability to help her.
I am usually the last one to vote for putting an animal down. If there was anyway around this I would push for it, but if you cannot afford the medical care to treat her, and the outlook is bleak even then… and not knowing the extent or details, your cat, at the very least, probably needs some pretty significant pain management, even if you did want to care for her at home, until she died, if you wanted to provide some kind of “kitty hospice” situation for her. She might need intravenous opioids even, just to see her through, until she died. You aren’t going to be able to do that for her. I wish there was another way, but I think your only option is to have her put down. I am so very, very sorry sweetie. :-( I just think it’s the only choice you have. Your cat is dying and is in pain most likely.
I have been referring to your cat as a “her.” My apologies if that is wrong, you didn’t specify.