The fact that she only touches or engages in physical contact with you when you're both drinking could mean a few things. A: She's not really attracted to you and when she drinks she's a little looser to the idea.
B: She is a little cautious about what kind of friendship you have and that seems to go away when you're both relaxed and having fun.
By judging from you're other post, you saying she hooks up with a lot of girls, I'm guessing A. Just a guess though, I'd have to see it to make a better decision.
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Semper Fi