Sorry but I don't believe the restraint came unlocked. I've worked a B&M and sometimes if the restraint doesn't quite click into the next lowest ratchet, it can pop back up to the next higher one. People always complain of their restraints coming unlocked but trust me, that is most likely what happened. The restraints on a B&M or any roller coaster really should never unlock during the ride. In the case of your step mom, I'm guessing the restraint popped up a ratchet and then she yanked it back down again and got the full click.
Yes, that's a possibility. It did pop up pretty far if not fully unlocked.