Why is she being distant and/or avoiding me?

There’s this girl I really like at work. When we first met, she talked to me a lot and was very flirtatious but at the time, I wasn’t interested in her at all and kind of just brushed her off (I know, I’m an idiot). We’ve since become good friends now and talk every now and then, but just recently she has given me the cold shoulder and will not talk to me, and actively avoids me now. She will however, take the initiative to say “hi” (in a very shy voice) to me every time we pass each other in the hallway or when we’re alone. But I don’t take it further than that because I keep thinking she doesn’t like me.

At work she’ll just talk to our other co-workers and avoids talking to me directly. I don’t think she’s a very shy person in general; she’s very social and talks to everyone in the company. Is she possibly shy around me now, or she is uninterested in me. I have not told her that I like her at all, and I have no idea how she feels about me. We have hung out a few times outside of work. I haven’t done anything to her to make her hate me, that I can think of, other than not talking to her much or ignoring her because I wasn’t sure how she felt about me.