I'm having a few problems with my mare, namely that she is fixing her neck to the right and becoming dead and heavy on her left rein. She is worse when out on a hack. In the school I can push her off my right leg and get her to soften in her left rein but on a hack she just seems to fix her neck to the right and won't soften or bend to the left. She is a 9 year old ISH, and is ridden in a full cheek french link snaffle. She has had her teeth, back and saddle checked recently. I asked a friend to ride her and he confirmed this and he found her quite strong. Any suggestions as to what I might try to get her to soften to the left?