It's difficult to say from a distance whether or not she likes you. I'd have to see her behaviour. However:

1. You're her manager.

2. She's got a boyfriend.

Both are excellent reasons not to get involved. The first because there's a difference in your level of power. The second because if she's willing to cheat on him, it doesn't show a great deal of moral fibre.

Not that I'd seriously judge her for flirting with you. Even though she's in a relationship, it's not like other people suddenly stop being interesting altogether. Usually complications are easy to avoid, because feelings aren't reciprocated. It gets a lot more difficult when someone she fancies shows clear signs of liking her too.

So, well, what is it that you want? Think about that, and act accordingly.