... I'd never mention it to him. Like I've said before, for reasons that I won't go into here, the husband is behaving as if he has nothing to hide and I don't really think anything physical is going on. I do think he displayed poor judgment.
If nothing happened and she didn't claim that anything happened, I reject the idea that poor judgement was used....even if 'nothing' was going on, this situation sure does look bad....NO WAY would I allow a teenage daughter to spend the night at an adult male's home....that just spells T-R-O-U-B-L-E!
Not too long ago, there was a thread about a dad needing some kind of out-of-state medical care and the mom needing to go with him. The problem was that she didn't know what to do with the teenaged child while they were out of town. The teen couldn't go out of town due to other commitments. As I recall, the solution that was suggested in the thread and that was implemented by the mom is that the teen stayed with a family friend. It's strange that in this thread that this idea is unfathomable.
Per the OP, a teen-aged girl spent a night at an adult's home and nothing happened. I fail to see the angst.