Why did she lose interest?

This chick at work came over a few times and we had a lot of fun. But the last time we worked together she dodge me at the end of the day but we ended up hanging out after work. Over the weekend she was sometimes mean to me but also teasing towards me. She ended up rejecting my advances that day. So I’m curious what’s going on in her mind and can I do anything?
Why did she lose interest?
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