Is her name Shannon?
This sounds exactly like someone I knew, who was convinced that we were the best of friends no matter how much I tried to show her otherwise. She might have been romantically interested in me, but I always played completely oblivious to any moves she made in that respect.
The sick thing is that this girl kept turning up in my life. When she did, she'd always try to talk like we were buddy-buddy. It was revolting. I mean, this is the girl who called my house, talked to my parents for a bit, then kept me on the phone while they went into my closet and found the carton of cigarettes I'd stashed there. I really despise her, even though I saw her last a few years ago. That time, she kept subtly trying to one-up me by telling me how well she was doing in life, how she had a nice new Apple computer and a good job.
She finally shut up when I told her about how I was basically living with and being taken care of by a 27 year old woman. (I was 19 or 20.) Haven't seen her since, and good riddance. Bitch.