It takes effort and work for a horse to buck, or crow hop - lazy horses, wont do it, because that means they have to put that effort into it.
I would get a vet out to assess her, or a Chiro to assess her back. Saddle fit, teeth....etc, etc.
She could be doing this, because she associates home with not having to be ridden because she hurts. When she's at home, she has no one on her, no saddle, no bridle, no weight bearing, etc, etc. Something to think about.