Okay first, either you hire a proffesional stal.. i mean.. detective. Or, you.. follow her.. around. Then, once you have enough information about her friends and her family and her habits, that is the time to take action. Go to her best friends house, get out some chloroform and gag her. Take off her clothes and put them on. Wear her make up, and infiltrate the facility of her hangout. This is where your secret agent skills must be used, to convince them that you are in fact, their trusted friend of 8 years. If questioned about your appearance, here are some useful phrases:
"I was hit by a car on the way here"
"I forgot my foundation"
"I was captured by alien monkeys who turned me into a transvestite"
Now you can get closer to the girl.. until BAM, knock her out with rophynol. Well either that, or surprise her with the fact that her childhood female friend was infact a man all this time.
If all else fails, I suppose you'll just have to wait it out until you can talk to her at school, or bus, on train. And don't be intimidated by her friends... but yeah, it is best if you talk to her in private. Bring along some cheesy pick-up lines and plenty of things to say.