Its not just Petco, every other pet store that sells animals has the same problems. If you want to see if she is getting the medical attention, go in there everyday and bug them about it and ask to see her.
Please read this thread:
Guinea Lynx :: Topic - Please help Shake Shake....... I dun wanna lose him
What happened to Vinci sounds about the same as your situation. He was able to get his(?) pig back and alive! Check it out.