Bought my boy a NEF Handi rifle in 243. Its perfect for him. Don't worry about it outgrowing her. You can buy longer stocks. If she ever outgrows it, you can trade it off too.

The 243 actually was too much for my 8 YO. the NEF is very light and has a very short barrel. The muzzle blast was significant enough to worry him. I have since reloaded some Youth loads for him and he loves it. I got the info from Hodgdon. 28.5 gr. H4895 with 85 gr. Nosler partition. Its recoil is more like a 223 now with very little muzzle blast. Perfect for a kid.