The first thing to do is to get the gun fit to her. If the LOP is too long for her, she will never be able to shoulder it properly and will experience excessive perceived recoil. I'm 99% sure that this is what is happening. If she still has problems after the gun is professionally fitted to her, try some AA low recoil or AA extra low recoil loads. I'm willing to bet that all it's going to take is cutting the stock down for her and her learning how to properly shoulder and fire it. I've seen plenty of small preteen girls shoot 12Ges just fine once they are fitted to them.
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