i'd say you didn't have a good grip with the dry hands slipping around. also well tucked under your arm. if she can't handel it you might have to go to plan B,,,,,get her a smaller gauge.
also looking around mossberg 510 min 20ga comes in 10 1/2 lop.
also looking around mossberg 510 min 20ga comes in 10 1/2 lop.