Hi there, like Tracie said its hard to diagnose the problem without seeing her ride. But from the pain you are describing it soulds like a combination of binding position and weight distribution. I agree with both Tracie and Johnathan that you should play around with her stance a bit, it takes a while to get it where you feel comfortable. Also, it sounds like she is riding back foot heavy, as most beginners tend to do. Something about leaning forward makes them feel like they are going to nose dive, so they put 90% of their weight on their back foot, and that puts a lot of strain on your back quad muscle, hip and knee. Have her try leaning more on her front foot, about 50-50 or 60 back, 40 front.
One good way to find out natural foot position is to jump off a chair or something and make not of how your feet are pointed when you land. Or if you are standing casually, see if you are duck toed or straight foot.
Hope that gives you a place to start.