Girls, Why is my coworker giving me so many mixed signals?

I have an older coworker who I really like but I'm not sure how to figure her out. She's pretty shy and awkward, but she can be night and day on me depending on the day. She likes to linger at where I work, taking her time before leaving, as if she wants me to stop her and talk to her. Sometimes I do, sometimes I don't just to see what happens. This is mostly because I want her to initiate conversation too. Either way I'm always friendly with her. I've caught her staring at me or even peeking at me before. But at the same time she will rarely ever wave at me or say hi unless I do so first. She basically acts like she doesn't see me. And sometimes when I'm trying to be cordial she'll give dry responses as if she's just not interested. But.. sometimes when I deliberately mind my business and reciprocate, she'll try to spark up conversation with me. To my knowledge she's only this way with me. She's either fairly chatty with some coworkers or completely dry and distant with others. I can understand her acting like this at first since we didn't have a relationship, but she still acts like this after we've built up a rapport. She clearly wants to talk to me, but then she'll It's definitely hard to hide my interest in her and I would be shocked if she didn't know, but I never go as far as flirting, because I don't know where she is yet. Can someone elucidate why she may act this way with me and honestly only me (to my knowledge)?

Girls, Why is my coworker giving me so many mixed signals?
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