WIBTAH for not paying vet bills for something that happened after the incident?

So a few months ago my dog attacked my dad’s cat which left her with a broken legs and some lesions on her belly and neck. She splipped out of my hands while being moved from the kennel outside to the house and ran straight for the cat under their house next door. When the incident happened, we told my dad and step mother we’d pay the vet bill because it was obviously our fault it happened and we have been paying them back whenever we could since then. The dog was immediately removed from the property and eventually euthanized after evaluations and training deemed her too dangerous to keep and no one else being willing to take her in for a second chance. Fast forward to a few days ago. My wife has kept up with our payments and had an amount she figured we owed but when I asked my SM for an exact balance, we received an additional two invoices for the cat needing additional x-rays and a splint replaced because she kept slipping out of it twice. This adds another $210 to our $1,400 balance we’re already struggling to find the money for. I will note we are 27 and 30 and living in an RV because we can’t afford anything else after a few years of hardship. My wife and I and a few others who know the situation agree it shouldn’t be our responsibility to pay for the cat being re-splinted after the fact so we don’t plan on repaying that portion. Are we wrong for not taking care of the full balance even though my dog isn’t the cause of her taking off the splint?