Do you know how to do a one rein stop? If you don't thats the first thing you need to work on. When she starts going faster than you want her to go or that you have cued her to do, one rein stop her. It sounds like she is just testing you and she has won so far.
How much training have you had in riding? Maybe you need to get on her back and spend a few days in the round pen or arena just walking around cones or in circles. Get your confidence in yourself and your horse in order. When she wants to turn for the gate, choke down on the reins so she has to keep going forward. If she starts going faster, one rein stop her and make her continue in the direction you want to to.
It sounds like she is just a bit barn sour and is seeing how far you will let her push you around.
Have you thought about taking some lessons with her?
"Until one has loved an animal, part of one's soul remains unawakened..."
- Anatole France
Last edited by Vidaloco; 04-13-2009 at 10:26 AM.