Is it ok to give an adopted pet back to the RSPCA?

[HELEN F]

We adopted a cat from them a week ago and all she has done since is vomit ! Ive had her to the vets already and she was given antibiotics and stomach drugs but she still isnt better, she has to go back again tomorrow. Its getting ridiculous, the house is ending covered in the stuff, my carpet is taking a battering with all the scrubbing!( must be 30 times now!) Ive already spoken to the rspca who say she has no history of the condition but this isnt what we planned when we adopted her. I know animals get sick and it would break my heart to give her back but if this is going to be a continuous occurance I dont see another option. Does that make me a bad person ?
I have already approached them re the vets bill but they arent prepared to help with the cost. Also it isnt the food as the vet has put her on a sensitive stomach diet but it isnt helping.
You guys are being so kind, Im sobbing now though at the thought of giving her back.