This is one of those things where it might be best not to surprise her with... women hold rifles differently than guys. You may want to take her shopping and find one that she things fits her comfortably.
Mike, Grand daughters are worse than wives or girl friends, they know how to con old grandfathers out of anything.Generally the youth models are a good place to start. Make sure it has a good recoil pad.
7mm-08 is not a bad choice. Avoid getting a gun that's too light; it will kick excessively hard.
You probably don't want to hear this, but you really need to start her out on a .22 (that fits). So that may be a better "first choice" if you don't have one that works well for her already.
If you do... then you'll have to get another one for yourself, she will claim it... ask me how I know!