Why she's spreading rumors behind my back and act sweet in front of me?

Okay I knew her for awhile nothing really between us I just took her once to the beach did walk there and talking on social media that's all nothing official between us.
I didn't talk her for long time as things didn't work for us. Anyway she's talking shit behind me Which I don't really care whatever she says but I just want to know why she's acting like sweet witch but in my back she talk shit !!! Is she afraid?
Why she's spreading rumors behind my back and act sweet in front of me?
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