[Chrysalis]

Seems I'm getting a partial story here so two ideas came to mind.

If that person did in fact spend time, energy and effort on your behalf, you do in fact owe money regardless of the outcome. No professional likes clients who refuse to pay and from her perspective, you might be in that category. If that is truly the case, pay her to clear up all that negative energy.

The other idea.

I don't know how it works where you live, but if you're 100% correct that you don't owe her any money you could go to a lawyer who gives free first consultations. A letter from a lawyer is usually sufficient to get another to back down. I do agree with keeping copies of your emails, etc you have between the two of you as it's evidence.

A smear campaign isn't a good idea as that piles on the negative energy which you want to get rid of. Not only that, if someone did manage to trace it back to you, such a campaign will not only backfire but turn against you.

The only solution I see here is legal recourse (police, etc) and some magic to cut the chords between you two.

I hope you resolve your situation soon.