I maybe wrong in saying this, but I would try to fix the problem before possibly shipping her back if that is an option. She may not make the trip back to the seller. If you cure her and all is well and still wanna send her back I would have the seller pay for the vet fees. But, I would also let the seller know that these are your intensions before you go ahead and treat the problem. Although if you are able to cure her you probably would wanna keep her and have the seller pay the expenses just because that's the right thing for him/her to do... Just a thought.