Ahhh...you are making perfect sense, A..
And I am in a bit of disagreement with a few of the other posts where they just don't do sleep overs. I have one daughter who is 18 and her best friend from second grade has been dealing with self-esteem issue, which can mostly be attributed (IN HER CASE ONLY DO I SPEAK) to how "strict" her father's rules were about sleeping anywhere other than their immediate family. Her father was abused by an uncle as a child and therefore he was truly trying to protect his daughter. What he ended up teaching her is that he didn't trust her ability to behave, stand up for herself, and further influenced her belief that she just didn't fit in with all of the other girls. Now, I know this is an extreme example but my point is to point out unintended consequences, and I believe when a child is restricted from participating in what our society considers a norm, unintended consequences will follow in some shape or form in their life.
Furthermore, I also believe you are spot on in meeting the parents, discussing your wishes regarding movies, television programs, music, ect. I think, as we teach our children, honest is the best policy!! Be up front,(and what a great way to reinforce to your daughter how important it is to be honest) explain the parents how you want your daughter to attend, but (insert humor) I am just one of those parents who needs to know the people who will be caring for my child. Someone suggested a playdate...and I thought that was great, why not meet for a picnic lunch at a park? I also agree that older siblings CAN be a red flag, but not always, in some cases a "good" older sibling can be a great role model for the younger kids. I believe that the biggest red flag will be that of a parent who doesn't appreciate your candor or your position, and in there lies the answer to the decision of that particular sleep over!
Finally, I would suggest resolve yourself that at some point while with her peers, be it at a sleep over or else where, she will be exposed to something that isn't acceptable by your own family standards. Use those opportunities for discussions which helps her understand why they aren't acceptable, find out her thoughts and emotions. Gently guide her through the process, which will help her understand why her values are what they are and why they work for her. She will be a stronger and better person in the long run for it. It also gives opportunity to discuss differences as simply that - differences. Your friend and her family are wonderful people, but while they think that (x,y,z) is acceptable - they may have something which is off limits that our family has no issues. Neither makes us or them better or worse, just different.
Best wishes!