It really looks like someones going to get hurt before she's going to realize her plain ignorance.
I would probably flat out, harshly, point out that she is pushing that poor horse to far to fast and is going to wreck her. That mare is either going to end up completely mind ruined or with broken bones.
Compare it to school. Ask her how she would like it if her parents forcefully shoved her through her current grade and straight into college, expecting her to know everything already.
Wait! I'll fix it....