I have seen people on DFP ask about the proper bat length and weight, etc,for their DD. Here is a You tube video of Michelle Smith giving her opinion of how to determine the proper bat length and bat weight for your DD. Hope this helps some parents out.
https://www.youtube.com/watch?v=OKMrpfQJyuo
https://www.youtube.com/watch?v=OKMrpfQJyuo