The other possibility is pain of some kind. Any change in tack? Have her teeth had their regular care? The long trail ride could have caused soreness if the saddle was not good in any way Does she run like this if another person rides her?
Maybe she has become more entrenched in the herd such that she is now herd bound, unlike when you first brought her into the setting. Maybe while she used to be more dominant, now she is more subordinant? (or the other way aroiund. Of course, this only really applies is she runs IN a herd.
On that bad trail ride, could she have injured her tongue during the fight you guys had to keep her in hand?
Just brainstorming here.
Do you have a place to free lunge her?