At ten years old, I would feel confident in letter her cut if you have given her instructions on safety and used some of the suggestions offered in this thread. If you get gloves, be sure they are small enough.. gloves that are too big are more of a hazard than no gloves at all.
I would stay with her and watch closely at all times that she is using the rotary cutter.
One thing you will need is a cutting surface that is adjusted to the correct height for her.
Dont insist that she cut it all in one setting. Cut a little and sew a little, just like we would do. Make her take breaks. I have a tendancy to work too long and can get burn out. Dont want that to happen to her, want her to come back excited to go again.