You need more control of his hip and more collection.
You get half changes when you ask with a direction change that throws his front end over but leave his hind end behind -- so to speak.
You can ask after putting a horse into a reverse bend, maintaining that bend and asking for the change by taking one leg off and putting the other leg on him beind the girth.
You can collect a horse in a counter canter and change legs to get a correct change. Both require good control of the horse's hip. You must be able to move the hip over into the new lead.
I must warn you though, the more you try to change with directional changes and more often a horse goes on while crossfiring, the more comfortable he will get crossfiring and the harder it will be to get complete lead changes out of him. Horses develop an aversion to lead changes when this happens and it can be very difficult to fix.
Since this is her horse, it is her problem. I would not try to teach this horse flying changes without her showing you exactly how she wants it done, either by riding the horse and showing you or coaching you while watching you work with it. You are in a 'no win' situation. You do not know how to do it, and it will be your fault when the horse only learns how to change in front and crossfire.
Last edited by Cherie; 11-04-2012 at 08:59 AM.