I would definitely ask them if she's going to be on the piroxicam long term, and if so, can she have a stomach protectant? Do you trust this vet? It seems like she is being treated for both a tumour and a UTI. And the dose of piroxicam seems too low. Very important she takes the piroxicam with food. And for the trimeth-sulfa important she drink a lot of water, so feed her wet dog food- ie. soak her kibble in water or give her reconstituted dehydrated raw or raw or canned food. And for the UTI you should be able to give her the d-mannose powder after the infection is gone.