My mom is backing out of paying my vet bills

My mom offered to pay for half of my dog’s surgery when she needed a bowel obstruction surgery. My dog needed the surgery because my mom kept buying her cheap toys after I told her for months to stop giving my dog these toys because she was literally eating them. I don’t think my mom put together that the bowel obstruction was her fault. (The object was a squeaker) Either she’s manipulative and playing dumb (she does this often) or genuinely hasn’t put together it’s her fault. She agreed to pay her half in full, but she backed out of that after the surgery was done. Now the pet hospital is basically making me sign up for a credit card that has horrific interest rates to pay off a balance of $4200. I am currently unemployed because of a disease I have. I’m not on disability because I’m newly diagnosed and haven’t spoken to a disability lawyer yet. My mom is sensitive, and she’ll be incredibly upset if I point out this is all her fault. My mom is also quitting her job this month without having a new one lined up. She has gone on 6 vacations this year. I don’t want to be an asshole, but she could’ve went on half as many vacations and kept her word that she would pay for half. I don’t know what to do here. I also feel entitled demanding that she pay for it because it’s still my dog.