Feet

Right now I've got a female former DI cross country runner that still trains like she's gonna lose her scholarship. We are seeing her for a torn posterior tib. Interesting, during the eval, her arches were almost exactly the same on both feet. One side she's had multiple stress fxs, plantar fascitis multiple times, etc. The other side, she's never had an injury. However she has always had orthotics in her shoes since her early years in high school.
Oh did I mention that her navicular has migrated medially and her talus pronates extremely bad.
If the feet were the problem, and she ahd orthotics in both the left and right shoes? Then why is one side never injured while the other is frequently injured?