I would say to wait until later teens- 16 to 18 years- for healthy body development. www.huffingtonpost.com/neal-m-blitz/girls-
My dd is 12 and also likes the idea of wearing higher heels but she will need to wait. I'm not going to have her deform her feet for life while they are still growing and also feel 3 or 4 inch heels create an inappropriate image for younger girls. There are plenty of attractive shoes with lower heels.