I look on it as the following...
a 12ga 2-3/4" loaded with #4 Buck (27 pellets) in my mind almost the same as the 18 shot of a Marlin 60.
As other poster indicate: First have a gun.
May I suggest an alternate? Consider the M1 Carbine with soft nose ammo and a lightly polished feed ramp to minimize stuttering. With a butt pouch attach, you can keep three 15 round magazines with it and loaded as desired, all 15 or less.
Good luck and get her to practice any time she can.