YA Fantasy novel early 2000s- girl held prisoner, escapes on one of two twin horses
This is a book I likely read in the early 2000s, it was probably YA fiction.
It was fantasy, sort of medieval style setting.
There was a girl being held captive somewhere. She is allowed out in a field to ride horses under supervision every day. She has two twin horses (I think their names were horse food related- maybe Apple and Oats?). While riding bareback one day, she discovers a form of trick riding where she can sort of ride on the side of the horse.
She makes a plan and then escapes by pretending to fall off the horse one day, but she actually just slips onto the side of the horse away from the guard, so he thinks she has fallen off somewhere close and goes to look for her, but she is still with the horse and rides off and escapes.
I have searched for this scene via google and ai but haven’t found anything that sounds right.