I have a freshman in HS who started playing 2 years ago. She's gone from a exhibition player to 2nd doubles to vying for the #1 singles spot. The only thing that's holding her back is her first serve. She hits good serves but instead of hitting with pace she hits with super spin. She can hit mega slice serves. When she hits topspin her serve reaches my head 5'10". I am trying to tell her to pronate (thumb up to thumb down) but this is only bringing limited success. I do notice that her dominate arm doesn't bend as much as I would like, but I am not sure that is the reason. Any suggestions?