Deactivate the flash and tell her to take the pic as soon as you hit the wake, that will give the camera time to think and take the pic when you're in the air (if you're using a digital)
Also, tell her to take tons of pics, so you'll have lots to choose from. With practice she'll start to get the timing just right. Oh, and if your camera works like mine, where you push the button midway to focus, and the finish pressing for it to take the pic, have her focus (press midway) first, before you start the trick and hold it and then just finish pressing when you do it. Hope that makes sense.
And last.... show us the pics here!