Romantic Gesture for Valentine's Day

This may be an unusual request but I need some advice on finding the location of someone. There is a girl in my class at University and I want to send her a card with a poem and a rose on Valentine's Day. I know that sounds really cheesy! lol

I planned to leave it at her front door when she is walking home from class. The only problem is I don't know the exact location of her house. I'm scared what may happen if share my feelings with her so I want to send it anonymously. I can't ask where she lives because that will make it suspicious and then she may know it's from me.

I have her mobile phone number and I am friends with her on Facebook but is there a way that I can use this information to pin-point her location when she is at home? The alternative will be to follow her home in disguise i.e. hat, trench coat and sunglasses, but that's just creepy! lol

I'm not a stalker, I just want to leave a card and rose on her doorstep on Valentine's Day.

Thanks for your help!