First, on dating someone from work. If she does not work for YOU and does not report to you in her job, but instead had a totally separate chain of command, it is OK (Unless there is some draconian company policy against it). In fact, I've read that the majority of people meet at or through work these days. (IMO, we spend too much time there.)

Then, how to know if she likes you. Difficult question. Best answer I know is this. If she shows an interest in you, your advocations, and interests, she REALLY likes you. I mean, long term. But if she does things like hair flipping, attempts to look sexy, and making suggestive comments (without the things formerly mentioned above), then view her as a temporary sort of matter, and don't be dissapointed when it turns out that way.

Hope this helps,
Richard