Why do some girls that are "taken" flirt with guys?

The other night I met a girl that has been in a relationship for a while, I totally felt a connection and she was very flirty. She was even dancing with some other guy before we started to talk, and my buddy tells me she is like that all the time. I can’t help remembering her eyes though, and want to follow up with her.. is this a BAD situation or a GOOD one?