Anonymous wrote:OP here. I don't particularly care about her use of electronics, attitude toward meals, etc. Those are all fairly trivial, and we will either roll with it or let her know if we feel that things are getting out of hand. I do care about safety, and that is why my position on alcohol, drugs, and smoking is non-negotiable. I'm not planning to staple a list of rules to the wall; I will have this discussion with the parents before the plans are finalized. We don't know the parents well, but having lived in Europe, we know that expectations regarding alcohol and smoking at least can be somewhat different and want to make sure that we are all on the same page. Asking about their house rules in other areas is a good suggestion, and I will start there.
I think it's fine to remind the family that since she is 15, it is illegal for her to drink or smoke in the United States and you expect that she will follow the law.
You might ask what their house rules are and what chores she normally does. I'd ask if she has a curfew and what it is, and see if it's something you can live with. You might discuss having friends over--for example, a reasonable rule is that she can have classmates over, but she needs to ask you in advance. Another reasonable rule is that you need to know where she is, so if her stated plans change, she must notify you right away.
Otherwise, I'd think that she just needs to clean up after herself, pitch in a little around the house (help set the table, clean up after dinner, that kind of thing), and be polite.