Can someone explain to me why the maid sally is bad? I dont get it is she a spy?

SO in the novel it says that the maid Sally is a spy from the ex-fiance, she is spying on Fl only because she herself is in love with ex-fiance.. and is willing to do anything for him, even when he is just using her and insulting her.

Spoiler..
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When ex-fiance gets arested and jailed, FL finds out that Sally was a spy but takes pity on her(remeber her past self), Sally is fired and banned from the household but given a large last pay and leave to travel fare away.

thanks!