My horse jumps like a racehorse!!!HELP

I recently started showjumping again this summer after months of mostly cross country. I wanted to do eventing. My horse used to showjump quite well before but she has gotten to a couple of bad habits lately. She jumps all her fences like a racehorse would, like through them. She does this cross country which doesn't get any faults but she bangs her legs of the bigger fences(1 metre-ish) a lot. I'm afraid she is going to injure herself one of these days. Now she is doing the same thing in the showjumping arena, knocking the top pole off 50% of the jumps. She not just clipping them either, she's hitting them with her legs sometimes above her knee. She just doesn't lift her legs high at all. She won't jump up if you know what I mean, more flat out. Another thing is I have to let her go quite fast to jump them, like cross country pace. If I try to make her come in at a nice steady canter she always refuses. She is a 9yr old part-bred 15.2hh mare and I love her to bits, but she can be a real brat sometimes.