Is this girl I like an attention / tease or does she really like me and is just playing hard to get?

Hi, there is this girl that I like at work, we aren't really friends because we haven't known each other that long. I tried asking questions about herself to get to know her better and she replies with sarcastic, smart alec comments as well as blushing. When I ask her what she is doing now that college is finished she says she is busy and doing stuff, she is always vague when I ask her about her hobbies and what she likes or dislikes. She seems kinda shy around men but is socially quite popular. Now that she has known me for a bit now and has chatted to me on facebook, which she doesn't do anymore, mainly because we are not online at the same time, she has started to flirt back. She will wait till we're alone and then do things like turn her back to me and bend over to tie up a rubbish bag, clearly giving me a view of her bum and then on several occasions will bend over pretty low in front of me to show . Then sometimes when I am standing still she will come up quickly and stand beside me with her blouse opened as a wide as possible with her hair messed up a bit. Then she always keeps saying things like "have fun" when she is in the company of this older woman at work. Then she only seems to flirt with other guys when I am right behind her and when she talks to me she likes to get real close, like as in hugging distance, and once when I was talking to this other woman at work who is really attractive, I caught her giving us two "evils". Yet when I try and flirt with her, like complimenting her or giving her playful punches she backs off but then later she still gives me smart alec, sarcastic comments about how good I am at such and such and teasing me about my work Performance. So is it just me, am I not responding to her flirts at the time which is while she is giving me hot and cold, or is she just messing with me and just wants my attention but nothing else, or does she like me but is a bit shy on how to handle it and is why she backs off? I also get jealous males at work who "" me which means that when I get some female attention of off an attractive woman they will try and end the conversation. Sorry to be a bore, I hope you can help me. Thanks.