We are a very conservative family and explained to our au pair during the initial interviews and selection process that we are not looking for an au pair who is coming to America to party and spend late nights out in American bars.  Our au pair told us she was also very conservative and did not embrace the party-girl lifestyle.  For the first 5-6 months, this appeared to be true, however, after meeting up with other au pairs in the area, she started to adopt this behavior on a routine basis.  Our au pair is 25, so we did not feel it appropriate to select her friends, however, it was clear that she found three of the worst possible influences in the entire cluster for our area.  After a few late night outings, our au pair appears hooked on the club scene and staying out all weekend on the street.  Since she is not working, and she is an adult, we can't stop her from spending her free time this way, however, it does become a performance issue on Mondays when she is tired and dragging herself through the routine.  We have had a wonderful relationship with our au pair until this behavior began, and when we voice our concerns to her she just nods, and says "okay", and then does it again the next weekend.  Despite being 25, this is very much high school girl behavior.  We are saddened and disappointed by this change in lifestyle, but we don't want it in our home.  It affects the way she does her job, and it set a poor example for our children.  We have set up a curfew, and she just stays out all night instead of crawling in late at night, and comes back the next day to change clothes.  She doesn't drive our car, since that has to be returned every evening, so she is not breaking our rules.   Short of just giving up and sending her into rematch before she falls asleep behind the wheel with our kids in the car, we are not sure what else to do.  Any input from host families who have dealt with this would be invited.