has a hat around here somewhere
Tell her you will take her to court if she doesn't stop.
In all honesty that's more bait to make someone angry. The statement that you'll take someone to court has little meaning nor attached threat when its an individual saying it. You can add a bit more sting by writing it more formally from the company rather than the individual (and the writing in itself is also upping the game some as you're creating a clear paper trail of communication). However if you've no reputation for doing it most will ignore it or just use it to fuel their anger/agression against you.
Now if its presented and written by a professional legal firm things change a lot. No longer is it an empty threat but an actual clear statement that you really will go through with such matters since you've already started taking legal council. You can see big companies do the same thing, any legal communication comes not from "the company" but from the companies legal representatives/division.