My 2 cents worth is that I would try to talk to her first before going to HR. Recognise that she is obviously hurting becuase of her experience of motherhood but ask her to recognise that your experience is different. Give her some clear guidelines such as "don't mention my pregnancy" becuase what is considered "negative" can be a bit subjective. I would document the date that you have this discussion and also write down what you talk about, in case you need to go to HR later. Best of luck!

Ruth