It is possible she slipped under the door, esp. with all of the commotion going on. Cats like being in all the action

The ASPCA was just trying to be helpful. They probably had information from the previous owners, or maybe Jenny was scared and freaked out when she saw a cat.

Is she part greyhound? I have ALWAYS heard that you never leave Greyhounds alone with cats (or smaller animals) because of their high prey drive. That they arent trying to hurt them, but if the cat runs, it might set something off. It is not the dogs fault, they are just playing. Just be careful, and be watchful. Jenny has killed before, so maybe she did that at the shelter. Who knows. I am just glad she got along ok with Tripod