Let HER try them
My vote is whatever SHE chooses AFTER trying a few rounds from each .
.243 , 7mm-08 , 30-30 , 6mm , 7 X 57 , 6.5 X 55 , . to name a few that come to mind.
And then there is the 7.62 X 39 [ I have a CZ that is a hoot to shoot model 527 ].
But find friends or a LGS that has them for her to try,and a youth model would be THE choice.