OP, I am also dismayed that your trainer did not address the tranter. Dressage begins with a forward horse exhibiting rythym. This horse is so behind the leg that she is 4 beating. Canter, as you know, is a 3 beat gait, and if you don't have that you don't have squat. This horse needs to be taught to go forward from the touch of the leg if she does not move out and stay forward, tap with whip behind your keg. Start in walk, then trot, then canter teaching her that she must move forward at a whisper of keg. Remember, she can feel a fly on her side, so she certainly can feel a gentle squeeze from your leg and know that it means to move out.
I am curious why your trainer disregards the horrible four-beat cancer and has you working on circle? Does she have an answer for this? Does she ever get on this horse and school her?