7x57 is a great round. PPU usually keeps a good stock and can be ordered. As for needing
the longer throat ?? The 7x57 has a decent length on the neck. Generally a SAMMI reamer
will let a 175 grain bullet be about .020" off the lands. But this can be misleading since
bullet profiles are all over the map.

Now if it were me, and being very popular again, I'd build her a 284 Winchester. If she
grows up with it, there's just more options. But again, Nothing wrong with the 7x57 !!