Im a girl and something that gets me all the time is when the guy is pretending to not look, so i have more time to stare. But then all of a sudden glances over at me to catch me staring. You can also yawn and see if she yawns too since they are contagious. That way you would know if she was looking when you yawned, but I have not tried that one out for myself yet. You can also look down as your walking up to her and at the last second look up and BAM catch her looking. Try these out and next time u catch her, just smile.