Dating

Was she jealous and why?

So I work with a girl who shows me signs of attraction. So sometimes I approach and flirt with other girls in the office. A few times I noticed as soon as I do this, she peeks out of her little cubicle and starts watching us and tries to eavesdrop.
Also once I approached her and another girl and started chatting up the other girl, she was looking at the girl with a very unhappy and mean face.
What is all this?
Was she jealous and why?
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