How do i defend myself from slander and harment?

Basically, I have been dealing with harment from my boyfriend's ex for the last five years. it has been crazy. she has done everything from try to fight me to hurt our kids, and to lie about me to him about everything. she has used my boyfriend's social security number and gotten credit cards and loans in his name, totaling 13,000 dollars. She also did the same thing to his sister. Most recently, his brother found out that she also took out a credit card under his name. She has told his whole family that it wasnt her that it was me and that she went to the police station and saw a video of me using the card (completely false). Now she is threatening to press charges on me, not exactly sure why. I just want her to stop and ive been told what shes doing is slander. is it really worth my time and money to get a lawyer and press charges for slander? what other options do i have?