As hard as it is to do, I agree - don't respond - just ignore her - that will drive her crazy. I had my husbands little friend text me on my birthday to wish me a happy birhtday - which I ignorned. And she is a real psyco - a 19 year old one.
Maybe you can even block her number, if you want.
Me:36 H:38 Together: 20 years Married: 16 years Kids: 13 & 10 yr. old Discovered affair: 1/10 H denies affair. Refuses to save marraige. Divorce filed: December 2010