6.5x55 may be a little better suited for a long shot on a mulie, and I am worried that anything bigger might kick her too hard and then she might lose interest. She is really little, about like my GF. CZ 550 is a good rifle in that caliber and is a good value for the money. Savage .243 should also be given a lot of consideration. Also, she might really like the feel of the Savage Youth Model in .243. My GF loves her Youth Model. I fully agree with you about Ruger... Good luck..

Vinny