Pain killers can also cause constipation - so that might be why she was so interested in her rear end.
While I've never had a dog break a pelvis, I do know about trying to keep a dog inactive that thinks they should be able to do whatever they want - and how much you fret over letting them move so much as an inch.
I would second the suggestion to keep her on a leash while you have her outdoors. All it takes is for something to grab her attention - and JRT's are quick! In this regard, you are much better off being safe rather than sorry.
There are toys that you could use to keep her mind occupied, and there are games that you can play with her that would not require her to be running around. These puzzles for instance:
http://www.dogsinplay.com/c-7-toys-t...FQMQswodEihYGw
Good luck and I hope she heals well!