My Daughter has shot a couple of AA 400's for HFT over the years since she was around 16, with some decent scores well into the mid fifties at one point at HFT.
When she occasionally shoots now (quite well), she uses a AA400MPR in a GINB stock and a small 2x7x26 burris on top.

She's 33 now but only small build, but she has shot pre charged since she was 8 years old. I wouldn't think of any other gun than a version of an AA400 for a 16 YO girl for HFT.
If you think she is serious after a while, LG110 Steyr with a light wooden stock might also work, but they are a pound or so heavier for standing.

The 500 series are same as a 400 series but with sidelevers, which are very nice too.