When you trot her down a straight away, does she prefer to have you always on one posting diagonal over the other?
When you back her up, does she lift some feet, but drag others? consistently.
Can she reach around to her side pretty far for a carrot on one side, but not the other?
when she grazes, does she stand almost always with one front foot forward, and not the other?
Watch her in these ways to observe one-sidedness and stiffness.