My advice . . . fuck her.
Ok, sorry, just amusing myself here. This more or less falls under one-itis, and I suggest browsing the many other threads on that subject. The problem here is, there's too much at stake, which raises the odds that you will blow it.
Random girl in bar = nothing at stake = more likely to have good game
Girl in social group = high stakes = more likely to blow it
It's that simple.
However, I am NOT saying to give up on this one. I've had many of these situations blossom into good raunchy times. I've had others go nowhere. The main thing is to ISOLATE. Isolation is always important, but here it's essential. You need to be in a situation where both of you are not under the scrutiny of the peer group, so the stakes go back down to a normal level, so you can both relax and be yourselves, and explore whether there's chemistry there.
Ask her out. Go somewhere beautiful where you can walk/hike/bike/jog/whatever. Take her hand and see what happens. Your best bet is to escalate physically, not verbally. Do NOT spill your guts. "Oh sweet Griselda, how I pine for your loveliness" is not the way to go. Holding her hand is. If she pulls away before you do, that is obviously a sign she's not comfortable with moving things in that direction. With the random bar girl I'd say wait a while and try again, but in this situation you don't want to make things uncomfortable because you're going to be seeing her again.
So it's a bit of a tight rope walk. On top of which, if you have a crush on her, you're probably placing her on a pedestal instead of seeing her for who she is. Make sure you are "offering value" guy, not "needy" guy.
I've been there, and I wish you luck. Worst case scenario, you totally blow it and move to a new town like Bruce Banner (aka The Hulk).
Haha, just kidding. If nothing else she'll be flattered. Good luck, man.
-Zen
