I agree with Puck. More impulsion. I rode a lesson horse that required a crop. Ahh, crops can be your friend! Give her a squeeze or kick (depending on how responsive she is) approaching the jump. It's okay if the trot feels a little fast, it'll just help her actually GET OVER the jump.
I think all of the members are telling you to learn to canter because they care about your safety. I trust that since your trainer is a professional eventer she knows what she is doing. But if you start jumping 2' or more without knowing how to canter, I would definitely consider a new trainer, just for safetys sake. Good luck!