I'm thinking this.
After you mentioned that I am not properly setting her up, I found this article online. I think it will help me. Get the Canter You Want
Seriously confusing article.
What gets a good canter? An active trot with the horse listening to the rider. Aids
Slightly flex horses head to the inside (corner of the eye visible - no more)
Inside leg on the girth
Outside leg behind the girth - slightly stronger than the inside to define leg lead
Ask just as you come into the shortside of the arena. Problems
Rider tipping forward when asking loading the shoulders of the horse
Dropping the rein contact - allowing horse to run into the canter - this is what I think your problem may be. Correcting
Think up and away from the horses head - keep the contact on the reins so the trot doesn't increase in speed.
Carry a schooling whip in your outside hand, use this along with your outside leg to set the horse into the correct sequence of legs.
Sequence of legs
Outside hind leg
Inside hind leg and outside foreleg together
Inside foreleg - also known as the leading leg.