This is a terrible situation. People get arrested for animal cruelty for refusing treatment to an obviously sick animal the way your mother is :(. I get the sense that this will only get worse if anything is said to threaten her or make her mad. Where is the lump by your cat's spine? Is it in between or near the shoulder blades? If so, it may be Vaccine Associated Sarcoma. I think you should do what was previously suggested and see if there are any free medical services for handicapped pet owners through Animal Services. They may even come to you to get your cat for treatment and bring it back. I've seen that done several times on the various Animal Cops shows on Animal Planet. Is there anyone else you associate w/, any neighbbors?
LaHoma