Two weeks before she leaves tell her you have a special night planned for her. Make sure everything (EVERYTHING) is planned out so she can have her special night. An expensive dinner won't cut it- I'm talking a long walk down the beer and maybe some chasing, a horse-drawn carriage ride downtown (if there is any), a fat little mexican singing to her with his guitar at supper, be creative.
Think like you have a vagina.
Motel too cheap and trashy, beach too wet/dirty/uncomfortable, with the parents home feels too wrong, and I could go on.
I would suggest two options. 1) Get a buddy to put a luxurious hotel in his name, but don't tell her you're going there for that. Have the room set up with candles (flower petals are too to the point) but convince her that you're drinking champagne or wine coolers or something just for a kick (which you really need to have) and then going hot tubbing (which you really should do at this hotel). It's a sure thing.
The second is a 50/50 chance, and that's setting up your room romantically without the rents home and doing pretty much everything there. Also depending on what kind of girl she is, maybe hanging out with friends that want to drink some might ease her up, but I couldn't tell you.
Otherwise the ackwardness will ruin you and you'll do what I did and loose my virginity on my sister's bed while she was out with her husband.... but through experiance a little lying made me a virgin again to test that strategy =)
...... I know she's 15, I've been in your exact situation. DO NOT, I REPEAT DO NOT get her drunk, especially if she tries to get herself drunk so she won't be so scared. It will ruin your relationship.
Look up some material on what to do once you get her ready for sex, but 99% chance if you do get in you won't hurt her for that long, haha.
