Harassment. Is the short answer to that.
I would think, if she's really behaving as you say, and she is literally never leaving you alone to the point of making fake accounts on social networks to make your life hell, going to your place of work etc. spreading malicious rumours about you I would think is slander, so really there's possibly a couple of things you could frighten her with. A solicitor will be able to confirm what precisely you can do. I don't know where you are, but many here in the UK offer your first meeting free, to give an outline of why you're there and for them to inform you whether they can help or not and what that will cost.

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