How big is the jar? If it's a nice big jar with a big opening it should be fine. Make sure she doesn't over stuff it with bedding.
I gave my Finley a big jar and put it under his bridge, because he's happiest when he has places he can hide. He loves it.
I do tip it up slightly so it has better for air flow.
I was worried he would move in and over stuff it with bedding, but I feel it for condensation and it's always perfectly dry. When he's hot he doesn't go in there anyway, and just flops on his belly outside.
