1. Your horse is excited. She needs to use herself to get over the jumps, not speed. That means that you might need to go back to flatwork. Her back end needs to be engaged when she's jumping. Often, with my horses anyway, they put their energy to jumping higher when we raise the jumps, instead of using speed when they jump lower.
Exercises: Think everything slow. Make sure you are sitting back with your horse under you. If she is behind your leg, then that would be a reason for rushing. Make sure your hands and eyes are up.
If you canter a jump and she rushes, make her trot the jump. Her trot should be even before and after the jump. Also, practice halting off the jump, getting her mind to focus on you.
2. She wants to get the jump over with. Is her tack fitted correctly? Are you interfering in anyway that makes her uncomfortable over a jump, and want to rush through it? Are you looking down and making her nervous? Make sure that it's not your position that is affecting her.
I hope everything works out for you. My best advice is to make her trot when she rushes. She wants to canter, so once she is responsive to you, you can let her canter slowly, while listening to you. Good luck! :)
