It's probably a combo of a bit she doesn't fare well with and too strong of hands. What do you mean by soft snaffle? Broken snaffles can be deceiving as they can have a nutcracker effect. Maybe try a Myler or a french link? You may have to try out a few before you find the one that works best for her.
And, forgive me, I don't quite understand what you mean by strengthening your outside leg? You should be focusing on your inside leg.
We are not human beings having a spiritual experience. We are spiritual beings having a human experience. -Pierre Teilhard de Chardin