Do I have to be nice?

Ok, so here is my issue. I forward an email to someone that I am not friends with anymore. I only did it because I couldn't remember her old bosses address or email address. I had a email about greyhound dogs that needed homes and I know they loved their rescued greyhound before it passed away. Anyway, I forwarded it and got a little personal "how are you" email back. Shit. Then she told me Happy Birthday on someone else's blog. Shit. Now, I have been sitting here trying to decide if it is in my best interest to respond. Part of me wants to and the other half thinks I've lost my friggin mind. I don't' hater her. I don't want to be chummy with her. I just don't want to be mean either. I have never been very good at tact. That is part of my problem. Does someone want to write a "not overly friendly" letter for me? Short and sweet would be nice. Thanks!