Once she gets out there and playing she will have fun. It is hard to tell a guy from a girl from a distance. Girls are just as good as the guys, maybe more patient at times.
Her starting equipment should be light so it does not wear her down during the day.
M4 is still one of the better choices for a rifle. Even a CQB length is light and can still reach long distance targets.
http://youtu.be/TkUhs8RcXc8
http://youtu.be/l7CVb9G_inU