I've seen that often, with children and grown women of slight build. It's net even a matter of strength, necessarily; it can be simple balance. Too much weight out front, and the shooter tends to lean back to compensate. Leaning back = missing targets = frustration.
Definitely a good point. That's my fiancee's biggest problem. The recoil doesn't seem to bother her with the light shells, but she just can't help but lean backward. She can't hold it up very long (left arm gets tired), and when she tries to lean into the gun, it throws her all off balance and she gets frustrated. I don't really know what to tell her to do about it except to put a counterweight on her rear end. I think a properly fitting stock would help a great deal, but most 12 gauges are still pretty heavy.