All horses are capable of flying lead changes but if your horse already knows how to do them on command....
1. Can you ask the other person who was riding her what que she used to get the horse to lead change?
Usually it's as simple as shifting your weight, a light tap on a cretin side or a movement of the rein, it just depends one how she was trained .
2. You also should look into some dressage riding to learn more... she may be trained in dressage. If she is it would be good for both of you to train in dressage a little. The disyplin of dressage can be very helpful to horse and rider no matter what you choose to do together (i.e. Barrels, jumps, etc.)
"It's a lot like nuts and bolts - if the rider's nuts, the horse bolts!" ~Nicholas Evans