Giving this further thought,
-the son has always had Dad available as a deckhand if needed
-what experience does the girlfriend have on boats
She could try to be of assistance and do something dumb that could get herself hurt, maybe Dad ought to invite her and Son out on the boat for a afternoon first for some additional training. You won't want her to get caught between a dock post and boat because she thinks she can stop it or get a finger pinched trying to put a dock line on a cleat at the wrong time. She needs clear instructions on what gets flushed down the head. A couple hours with the two of them and then turn them loose.
I like this. Good time to spend with the 2 of them if it is serious. Maybe invite her father too if it is to that point. If not, no loss. Curious to hear how it went today.
Mike