I'm a horrible friend

I've been having a particularly hard time lately with a lot of personal things and then on top of it I got AF and an invitation to baby shower on the same day. Unfortunately my hormones and emotions took over my common sense and I made a rude and hurtful comment to the mother to be. Completely not on purpose and unlike me. Today I got an email from her stating that what I said did indeed hurt her feelings. I know I need to call her and apologize because I was in the wrong however nobody knows that we are TTC. I think this is part of why I flew off the deep end because I have no outlet. How can I apologize without explaining why I freaked out?