I would be *very* cautious about this. There are a lot of questions I'd want to answer before saying yes.
Will they be with his family the whole time? Do you know his family? Do you feel you can trust them?
Where exactly will they be staying? Is it a safe area? Can she get home easily if she needs to?
If it were my daughter I would not let her go unless I could answer yes to all of those questions without a doubt. (even if she were just going to be a few blocks away, let alone in another country!)
That being said, it sounds like you really trust your daughter and think she'd be mature enough to handle it. Otherwise I'd bet you wouldn't even be considering letting her go. It does sound like an amazing expirience for her. I hope it all works out.
Btw...

to JM. Looking forward to getting to know you better.