Remember Whose Roof You're All Living Under
She may be grown up and (formally) on her own, but this is still your house. It doesn't matter if she's 13 or 30, your daughter can't just do whatever she wants. She may not have assigned homework times and a strict, no-more-than-60-minutes-per-day TV rule, but that's no reason she can't tell you where she's going or call you to say she won't be home for dinner -- or even sleeping in her own bed tonight. These conversations may be a little awkward for both of you, but it's better than waiting up until the wee hours of the morning, worrying about her safety.
A few childhood rules still apply. Dish duty should still be mandatory, and there's nothing wrong with asking your adult kid to take out the trash every once in a while, too. Most importantly, if your boomerang child has an income, charge her rent! The extra funds will help cover the costs of housing an additional person, and paying up will help prepare her for the responsibility of living on her own (read: she'll be less likely to need to squat at your place in the future).