Join Date: Aug 2008
Location: Canberra, Australia
Firstly, don't let her run. If she starts running and you let her do it then she will always do it. When she runs pull her in a circle and then push her out with your inside leg, but don't start pulling on her mouth to slow her. Do a lot of work getting her moving of the leg straight away, like walk to trot transitions. Don't just kick her either, squeeze lightly, squeeze again and if she doesn't move straight of get a dressage/schooling whip and tap her behind your leg. If she's not used to that she should jump right of it. She will learn to respond to your legs more eagerly so you will not have to chase her into a canter.
Then make sure that your canter aid is significantly different from a go faster aid, and exaggerate it if she won't listen. Hold her head and keep her on a circle so she doesn't run.
If you think that her reluctance to canter is due to balance or something like that, then take her out on long and straight trails, and push her to a canter, or the hand gallop, and keep her at it for long distances, reducing her speed to a manageable canter, so she gets used to that pace.
If these do not work then you can try and teach her walk to canter transitions, but that may be difficult if she does not really understand that aid, but cantering from the walk can help a lot with the running.