I had a 1300 a few years back and NEVER had it do this! I've shot a pump all my life, so being unfamiliar with a pump doesn't factor into it.

Is she pulling back on the forestock when pulling the trigger? The action will release when the trigger releases and such an action may occur then. BUT if the forestock is sliding back WITHOUT input from the shooter, then in my opinion, you have a real safety issue.

Dunno!

I'd check with Winchester.