How big is she and how much recoil is too much? A simple matter of physics, the heavier the projectile and the faster it is moving when it clears the muzzle, the more the felt recoil all other things being equal. Absent a sabot, the lightest projectile will be the PRB. Assuming the guns fit her equally well, I would pick the gun that has the slowest twist rate, and if both the same, the heavier gun. I believe with reduced charges the faster twist can still deliver reasonable accuracy, at least at the ranges we are talking about here. I have a light TC New Englander .54 that rattles my tooth fillings when loaded with 100gr Pyro RS behind 435gr Maxi Ball. I wanted a 50 yard PRB load for jackrabbits, but rather than fiddling with the sights that were dead on at 100 yards with the hunting load, I backed off the powder until the PRB found the x-ring at 50 yards, which is a 40gr charge. Recoil is about like an M-1 carbine and it makes clover leafs in the 50 yard target.
Good luck to your young lady on the hunt.
