How do I find her?!?

in high school some stuff happened. There was this girl and I’m sure she had a crush on me. She would always stare at me and got really nervous then I came around. I am also a girl. We went to a really conservative school but she made it very obvious that she liked me. Her family is very religious. The way she stared at me was insane and she would try to talk to me and get close to me for stupid reasons. One time she saw me walking and went the other way. A lot of stuff happened. I secretly liked her but never did or said anything. She left the school and I graduated and it was too late. I have a boyfriend now and I really do like him. However I still think about her and stalk her page. I Imagine what my life would be like if we got together. She is in college now and when I look on her page she’s made a lot of new friends and isn’t as tomboyish as she used to be. I’m almost 100% sure she had feelings for me. I always think about having sex and doing stuff with her and I can’t control it. My sister is graduating next month so I am hoping maybe she will be there but I don’t think so. I’ve been thinking about her night and day. I know she liked me and kind of feel sad because I wonder why she never added me. It’s been like 3 years and I don’t know if she will still be open to me or not. I’ve thought about adding her but is it too late for that? I don’t want it to backfire but I need to know. We live in the same city and both will be home for summer, how do I find her?