I am being stalked.. How do I get her to stop?

If your lucky it will finally stop without involving anyone, but you might want to call police and let them know what is going. Chances are she is sitting outside listening to what your saying and knowing then where your going. I been through this exact same thing (with my ex but he was not married) so I know exactly where your coming from, it is scary. She may feel you contributed to her ending her marriage, since you mention she came around saying she was ready to leave her husband. Maybe she feels your responsible for all of it, or she thinks you will want to be with her if you learn she is totally single. Don't give her hope of any kind, don't speak with her or even look at her meaningfully. Any kind of kindness from you is taken by her to mean there is some hope of getting back together.