That's a horrific place to be caught mikedhf. This is a secret which can not be kept and if left will only fester and grow. I'm a great believer in getting things out into the open no matter what the fall-out is. Love will always prevail in the long run. Whether it is a conversation with all 3 of you or just a conversation between you and your step-daughter, I think it needs to be done. At least it is 'out there'. I would focus the discussion around the areas that are of true concern to you and not allow the conversation to be distracted by the more minor things eg hearing her have fun with herself. At the very least you will have established some ground rules.