Ex-husband's wife wants to be Grandma.

My ex-husband's wife wants to be a grandmother to our first grand daughter. This makes me so angry. This is that same woman that got pregnant for a married man and helped to break up our family. I don't only blame her, that's why we're divorced. This took place seven years ago, and although I'm over the break up with him, I still feel some kind of way about this womans impending involvement with my first grandchild. I know I may sound like I'm being immature, but that's truly how I feel. She has never done anything for my daughters to show that she wants to be a part of their lives but now she wants to be known as "Grandma" by my first grandchild? I feel like I'm going to blow a gasket!!😡 My vindictive ex-husband would have our granddaughter calling her grandma just to spite me. Am I being childish or are my feelings legitimate?