she's trotting over the fences because they're little and she's bored. That's ok. It means she's ready for more. More does not mean higher! First of all, if she lands at a trot, ask for the canter immediately. Eventually she will start to land at the canter. Make sure she is going at a forward marching trot to the fence.
If she's getting bored instead of raising the fences mix it up a little. Go over the jump (ask for the canter then back to a trot) and do a serpentine or something and then go over another jump, do another exercise, and go over another jump. That way she's always thinking and ready for the next move. One of the things you need to teach a green jumping horse is that they need to keep going after the fence and always be looking for the next thing to do.
And remember, you cannot ever let your emotions get in the way of your training. if you ever get so frustrated you're going to affect your horse's progress, it's time to get off.