I contacted her a number of times and each time made me feel better. The first time was to respond to her desperate email to my husband to get back together ( I told her she was free to have him, it was my DDay moment.) He'd broken up with her a few weeks prior, using me as the reason for the break-up. I let her know I was dumping him (didn't in the end) and that they were free to continue. Too bad for her to discover that he didn't want to!
Later I emailed her to let her know I was notifying her husband (that was fun!).
Then I just had some things I wanted her to know about her "relationship" with my husband. My husband has SA issues and was calling her 2 - 10x a day for phone sex. He was eventually honest with me about his addiction and provided me with concrete details of why it was an addiction, mainly all the things that repulsed him about her and why he continued to have sex with her and call her anyway. I thought I'd like to share these details with her. That was also fun, my relaying his comments made her see that their "secret" and sick relationship had been totally exposed and that my husband let me inside their affair, every small sick detail. I shared these with her husband as well. I had the added benefit of ruining her self-esteem.
I thought that her hearing all this would keep her from wanting to talk to my husband again but she just recently emailed him (blank, "fishing" email.) I forwarded that from his "secure" work email to her husband along with a supportive message to her BS, letting him know that we were doing better than ever and didn't want to hear from her again.