In an ideal world, your daughter's agreement with the principle would give her the strength to say no to these guys' self-invitations. Obviously she is not there yet. So how about you give her some help?
- Re-emphasize your concerns with her, and tell her you are willing to help her learn to say no if she is willing. Get her strong agreement before you continue--it may help to remind her of your earlier punishments and threats.
- Tell her that you want her to set herself and her friends up. On a prearranged day she lets the guys invite themselves over. Twenty minutes after they arrive you make a surprise stop at home. You find your daughter and the guys in the house. Then, according to plans, you get into a major screaming match with your daughter. Do not hold anything back. Then, after they have heard a bit of the screaming, kick the boys out of the house. Keep up the screaming until they are out of earshot, and then break into the laughter you will have both been fighting during the entire scene. Finally, take her out to dinner or whatever that night.
- The next day, or that night on the phone, she can tell the guys what a crazy mom/dad she has and how much trouble she is in. They will believe whatever she says, and as a result will be far less likely to pressure her into these home visits. (If on the offhand they continue to pressure her, then it will be clear to her that these are not friends--she will put this together on her own.)
I know the preceding sounds a bit bizarre, but believe me, I have heard many successful stories about this type of scenario from numerous parents. The key is that you are supporting your teenager's developing voice of responsibility. In many ways you act like training wheels for them--they get to borrow your guidance and balance while steering the bike. The nice thing is that even if she does not go along with the plan she will feel your support, understand the seriousness of the violation, and be more apt to control the behaviors herself.