Fair curfew for prom night?

Tomorrow is prom and my daughter is a sopre but is going with her boyfriend. The transportation is taken care of as they are going wit a group of kids and all the parents chipped in to rent a limo. The prom is 20 miles from here at the college campus in a banquet room and will be over at 11pm, until that time no one is allowed to leave the prom once they get there as this has always been the schools policy. One of the other parents is hosting an after pom party and this is where I get concerned. I know I am over protective of my kids, but the limo will drop them off at this kids house and from then on they will be in their own car. My daughter asked to be allowed to go to the party and said they would be home by 1:30am. My husband and I can agree on her going to the party, we know the parents and know no drinking will be allowed etc the problem is we do not want her in a car that late because even though this group is not drinking others will and feel like it is an accident waiting to happen. I know prom is special so what would be a good cmpromise.