Ninja Gaiden 2 got some HARD achievements, Prototype-clear the campaign without dying and Left 4 Dead- Nothing Special.

VIva pinata
Castle Crashers
Small arms (much like super smash)
a racing game is probably good(if she likes that ofcourse)
some of those Disney Movie based games is really good
if she likes beat up games where she can click whatever she wants try Soul Calibur 4 thats easy but it is 16+ though but i think she'll like it if she doesnt mind some violence(no blood though)

Fable 2
Bionic Commando
Call of duty 5(sold it after 3days)

Ninja Blade, Soul Calibur IV and Turok was actually nice. (but the guys that plays turok online ruins it though)