A darting glance, or a quick look followed by the person looking away means nothing on it's own.
Remember in flirting we need to rely on the rule of 3 to 5 signals or a cluster of signals and I don't mean one per hour.
If she looks at you, then looks away then doesn't look back, it's unlikely that she's interested as one look was clearly enough. Or she's incredibly shy.
However, if she gives you a darting glance, looks away and then looks back within a minute or so and holds eye contact, or plays peek-a-boo with a smile darting on her lips then look for these other signs to see if you're in luck.
Is her body pointing towards you? If she's not then chances are she's flirting with someone else.
Is she smiling? Eye contact without a smile attached can be a little spooky, but a full blown smile is more likely to signify friendship than attraction. When we're attracted to someone we are less likely to smile with all our pearly whites showing, but rather favor the half smile, perhaps with a lick or bite of the lips.
If you're getting repeated eye contact and other positive signals (at least 5) simultaneously then chances are you're in luck. Go up and say hi, or if you've already started chatting do the whisper and lean to guage her interest.
If she leans in, touches you or brings her head closer to yours, then there's definitely attraction there.
