Smohr,
I just got off the phone with the vet at Purdue University. They have a 24 hour vet clinic. They are among the best in the country. Anyway, she told me that she feels very confident that they lied to you, and that Petra is coming out of a sedation. She feels that if they truly euthanized her, she would have been in the freezer. She said that if you were with her the entire time, and they listened to her heart and told you that it stopped, they were lying. She told me that you should call the police immediately. She said that there isn't anything they can do, but it is the first step to getting this reported and preventing it from having it happen to anyone else. She said that as soon as you can, get Petra to the vet. A vet that is NOT associated with the vet that did this. She said if there is one available, even if its far, it is worth it. Although, she feels pretty confident that they just sedated Petra and told you they euthanized her, so she's probably fine, just coming out of sedation. you are doing the right thing by giving her oxygen..probab ly not the water though.
She thinks that they probably wanted to keep Petra for breeding or for a pet or whatever, and is HIGHLY suspicious. If you want to, PM me your number and I'll call you and tell you more, or give you the number of the vet that I spoke to...