Good morning.
I need a weekend to recover from my weekend, but am otherwise unscathed by party followed by sib visit 
Missy, perhaps your H’s objection is that at home, she has somewhere to eat and sleep at no real extra expense…and he’s not optimistic she’ll find a job a this late date, which would then turn the venture into a summer vacation compliments of the folks, as opposed to a summer of industry to contribute to her school expenses 
If that’s his concern, he could suggest to her that she find the job (remotely) in said town first to cover the nut, then present her accommodation plan.
Of course, my theory is colored by my own experience, and my own early workaholism, and recent observations of young college students living away from home to be with BFs 
McSon’s gf is adorable, and I love her, but she is seriously under-employed and was given parental blessing for a similar plan this summer. In her case, its a bit different as she does struggle with rheumatic arthritis, so jobs that are physically demanding are a concern for her. Nonetheless, I think in some cases if one has the opportunity to get by without working, they will. Its just human nature. Industry is something that is habituated, and often by necessity 
However, I think that can set a pattern that doesn’t serve young adults well later in life. I think its better to raise the bar and expect them to do something industrious or meaningful, or CREATE an opportunity for industry or meaningful contribution. It doesn’t have to be about money. Its more about the sometimes hard task we all face in inventing and reinventing a life wherever and whatever the circumstances, and feeling good about action to sustain ourselves.
I don’t know if I’m explaining this right and probably sound like something of a Calvinist, but its not quite that harsh 
I am thinking more along the lines of a combination of depression and inaction that can deepen when couch-surfing and not having the rudder of a schedule or purpose. I don’t have to think too hard to remember such feelings from my late teenhood during the times I willfully chose to be away from home but was at loose ends. Or observing my one sister who floated that way quite a bit.
Maybe these are things your H is thinking about, but is afraid to say, since his vantage is unique as a Stay-At-Home-Dad. Then again, maybe her absence forces HIM to also reinvent himself a little, since he derived his own sense of purpose from that role and she is the last real dependent. That can be scary too. Might be good to check in with him to get a bead on it all.
So either way, I’ll just send the mojo for a resolution that works for everyone 