Be supportive of her and let her try out. Unless there is a medical reason for her not trying out then I'd let her go. If she makes it, she'll have so much fun! If she doesn't, then she might learn something about herself. I think if you shelter her though and don't let her try out, you're doing her a dis-service.
On a side note: My daughters did cheerleading with Texas Cheer and Dance. I have one that's not very coordinated. They taught her how to work with her body. It gave her confidence and she had so much fun!