Self Defense for Children

I personally would suggest 8-10 years old she should be starting in a martial arts to keep her flexible as to when she would be very much capable in learning by the age of 12-13 she would not have a hard time in areas, like flexibility, speed, and coordination. she would now be only focusing on proper techniques executions and maturity to the art will come through the years. Try cross train her in different arts also to be more well rounded.

I think you can start whenever, maybe you could go with something like karate? That way, she wont think of it as being self defense classes but something more she can get in to, that she'll enjoy but it'll also keep her active :) The earlier she starts, the more likely she is to stick with it & become very good at it while staying healthy! There are other forms of martial arts which are good for self defense & good for staying fit, so maybe you should check out each of them individually & see which ones would best suit your child's flexability, endurance & patience!