D.D.
Yes it's their job to drive you nuts. Your daughter is normal. In my house we always say 'with rights comes responsibilities so if you want the right you have to take on the responsibility.'
Our job as parents is to give them the ground rules of life so that by the time they reach adulthood they can make good choices and be able to analyse situations based on facts and not just emotion.
1) Her prom choice doesn't involve you at this point. You have already told her that you will not spring for another dress. However you should be able to go to the friend's house and take pictures of the kids all dressed up and leaving. Getting dressed as a group and group pictures are common in CT. When my girls went to prom I had a half dozen parents here taking pics.
2)Rethink your curfew. My kids never had a curfew because I found out an interesting tidbit from one of their friends. He had to be home by midnight so he'd stop drinking by 9:30 and would be sober enough to go home by 12. Instead base your when to be home time by what your daughter is doing that night. Homework at Mary Smith's house? Be home by 10. Hanging out after school with a group? Home by 9.
3)Continue to talk with your daughter about underaged drinking but don't get sucked into a debate over drinking at age 18 just because you can join the military at 18. You don't make the rules so 21 is the magic number.