How can you tell if a girl really likes you or is just a flirt?

So ive known this girl for a while but i hadent seen her for like a year until a few days ago because we went to different schools until now. So we meet up for food and she gives me literally every sign that a girl likes you. she laughs hysterically at my jokes, she touches me randomly, her pupils dialate a lot as she looks into my eyes for long periods of time etc. But i asked her out a long time ago and she said were just friends. i dont get it! she acts like she wants me but she doesnt!? what can i do to figure this out?