Try classmates.com and other social networking sites. If you have a name see if you can find out associates near her on FB and see if you can have one contact her to contact you...you can do this via private messages BUT I would not disclose to these strangers your need to locate and talk her...I would just say that you know someone in common and that you both need to talk about something important...
I know when I was looking for my MIL (my husband was seperated from her at a very young age) I managaed to find an ex-wife of her deceased husband, she was very helpful in helping me connect with my MIL...using last names you can make phone calls in the area where she lives and possibly locate someone who knows her that will pass on your contact info or give you another way to contact her privately.
Just remember, where there is a will there is a way and I seem to think that she would very much want to talk to you!
