Hello, My name is The Pope and I've been a recovering long hair addict for as long as I can remember.
To prepare for such unplanned chance encounters I always do the following.
Wear short sleeves shirts (you can roll up long sleeves)so I have an oppurtunity to squeeze by next to her and cop a arm feel(works great in a night club even if she's with someone).
Always carry a camera.
Go buy a rose (or simular) and offer it to her (you'd be surprized how many women have never had a rose given to them). You just might become an "Instant Hero".
Regret is a terrible thing so take the chance. At least you tried no matter what happens.
Good Luck,
The Pope