Rushing 2-3 strides before the jump?

I had my best lesson yet today and I cantered a Jump for the first time! One thing I really need to figure out is how to make my lesson horse slow down, and keep an even pace all the way to the jump. We are jumping a crossrail with a one stride to a vertical, and then cantering around to about a 2' fence. She is slow and is listening to me as we approach the jump, but about 3 strides out she gets really fast and I try to slow her down and then I kind of forget about my position and struggle to get it back after the fence. I tried half halts on the approach but I don't think I am doing them right. Any advice/suggestions? And she is not my horse and I only ride once a week so is hard to work with her on things like this.
Thanks!

Anybody? : )
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Hmm ... I would just ask your trainer why she rushes the jumps. It's not your responsibility to deal with such a bad habit, and definitely nothing you can cure not being the only one riding her, and only once a week. Just talk to your trainer :) It's not a bad thing - you can learn from it. Don't be shy!

This is definitely something to bring up in your lesson as from here on out in jumping you will experience this problem. There can be several reasons for her rushing. Your mount may be unbalanced at the canter, nervous about jumping for a variety of reasons, you could be goosing her, or sharing your nerves with her. As your trainer knows this horse best, he/she is the best to solve this issue.