Hip/Rear Strength

Hope this is the right place for this...

Kona had a TPO about 1 1/2 years ago, and it has been a SLOW recovery process. I was wondering if anyone had some good exercises to help build up the strength in her rear end. She is fine for walks and normal day-to-day stuff, but in training it is really holding her back. She will sit slow and off to the side.

Any suggestions?

Thanks!