I don't have time to read all the responses and I'm sure someone else noticed this but, it sounds like you waited too long to hit her with the "let's get out of here" move.
She wanted to leave with you but couldn't leave with you as her friends were leaving too (they would see her after all).
If you had pulled this earlier I bet she would have gone for it and could have slipped out unnoticed or at least given a plausible reason to leave to her friends.
I think it was her friends judgement that you needed to circumvent in this case and because you were drinking and not used to a girl being ready to bounce you didn't act on it.
She wanted to leave with you but couldn't leave with you as her friends were leaving too (they would see her after all).
If you had pulled this earlier I bet she would have gone for it and could have slipped out unnoticed or at least given a plausible reason to leave to her friends.
I think it was her friends judgement that you needed to circumvent in this case and because you were drinking and not used to a girl being ready to bounce you didn't act on it.