I went through the same thing with my oldest. I never asked him who he was with or what he was doing as long as it didn't affect the whole family. I did have a midnight curfew because we worked early and didn't want to be woken up by someone coming in the house at all hours. If they weren't going to be home by midnight they had to find somewhere else to stay the night. It is a common courtesy for her to communicate whether she will be home or not. The rest of it simply is her business as long as it doesn't affect the family.