Honestly, very little.
Getting her worked up before hand is really a waste of time. As this show (Concert? Opera?) will cool her mood. i.e. shes unlikely to want to ditch whatever it is to go have "the sexy time"
I'd suggest meeting her a little before the show. (not 2 hours) Then going somewhere else afterwards. (venue change) That's when you need to turn it on a bit. Kino, sexual innuendo, etc. However, unless she's sick of her BF you're really going to encounter a lot of LMR before anything physical. So be ready to ramp it up slowly and use push-pull "Hey you're a good girl and I respect that" Oh, and as ever USE PROTECTION.
Just a small note. Alcohol on is own only reduces inhibitions. It doesn't make a girl want to sleep with you just because you're standing with her. You STILL have to seduce her.