I have 3 daughters. 28, 21 and 19. And a son, 30. I would not have allowed my daughter to spend the night w/o parents and certainly w/ 'the boys'. (Would you let your daughter have friends spend the night at your house w/o you there? Would you let 'the boys' stay at your house?) I would not have yelled, acted shocked...just say 'well that changes my decision a bit'. Yes, she could have not told you the 'special' circumstances of the over nighter. But she did and you need to base your decision on that. I have found that my kids sometimes were uncomfortable about being in certain positions and used me as the 'excuse' to get themselves out of precarious situations. I've always told them that they can blame things on me if they don't want to participate in something but feel peer pressure.