Check out Track of the Wolf. Get a replacement front sight file away until she shoots where she needs to. If the bullets are grouping okay, then obviously you need a lower front or higher rear sight.
Another thought: what load are you using? 1 1/2 times the caliber should be plenty for hunting, which comes to around 80 grains of black powder for a .54 rifle. If you are cranking 120 grains through, it may be that your velocity is so fast the bullet is out of the barrel before recoil can kick it up.
=WH=