I'm sure this girl has a boyfriend, but she seems to be attracted to me.... what's the deal?

So here's the deal:

For two summers now, there's been a girl who's flirted with me at a golf course I frequent. She happens to be a waitress there.

I wouldn't be a bit surprised if she has a boyfriend, but she seems to like me. I've caught her staring at me more than once, and even overheard a fellow waitress say something to the effect of "There's your boy" one time when I was coming back to the clubhouse for dinner after playing a round.

We've exchanged flirty comments back and forth. I understand why she might be flirting (for the sake of it, just doing her job, etc.), but she's got me a little confused.

I don't have a lot of experience when it comes to relationships, so I could be overthinking the whole situation for all I know. Is she just being flirty to be flirty, or is there a reason beyond it that I'm not picking up? And, if she does like me, how could I tell if she wanted to be with me despite already having a boyfriend?