When we first got Jackie, we had 2 gerbils (who have since died of old age
I miss my boys), and I let Jackie sniff their cage, and them while I was holding them. But she seemed a little too excited about them, so I never took the chance of putting them on the floor, or in their balls. I don't know if she would deliberately have tried to harm them, but they were so little and delicate, I couldn't take the chance. Your sister is a very forgiving person - if you had tried that with one of my sweet boys, you would have been staring at the business end of a hissy fit!
Very funny story, though (since it didn't involve MY pets, and it ended happily).
I hope that Foxy Brown was not too terrified. Jackie is a hoarder too, but mostly with her stuff. Sometimes she likes to stash her treats for later. She hides them in the lining of her bed.