I recently purchased a guinea pig from Petco. I noticed that she was making a strange sound when breathing.?

Called Petco, brought her back to the store within the 15 day treatment policy. They are keeping her for 2 weeks, treating her for an URI after taking her to their Vet. We really want her back. We are able to give her the medications and TLC needed, especially for a 2 month old guinea pig. We have been visiting her daily at the store. 4 days after starting treatment, she is no longer making a "noise" when breathing. Has anyone ever had this happen to them? I know they are following "policy" but why can't we care for her at home? I guess we should have just taken her to our Vet and paid for it.