Mrledzeppelin said:
look at the way she has her wrists when riding. they should be fairly straight. I switched to ergon grips b/c my wrists were bothering me and I love them! There are other companies making similar grips but the quality doesn't look as nice. Also make sure she is using her elbow and shoulders to act as suspension and not her wrists.
That's what I was about to say. There could be something wrong with how the bike fits her, but it could also be the way she is riding. Some people lock their elbows when they ride, which then forces them to ride with their wrists bent backwards. This is bad technique, and it is bad for your wrists and elbows. As Mrledzeppelin said, look at her elbows and wrists when she is riding. Wrists almost flat, and elbows slightly bent. Not only does that keep pain away, it also makes it easier to control the bike.
edit: oh, and support your weigh with your core muscles, not your arms