NTA. She isn't approaching it well, but she may well be concerned that you will have regrets....it may not seem like it, but at 28 you don't have but so many prime years left if you DO decide to have children. We had our first when I was 33 and my wife was 34, and our second and final a year and a half later....by the second, my wife was considered 'elderly' in the context of childbearing, which includes greater incidence of birth defects, harm to the mother, etc.

She could also be a busybody who wants her grandkids now.

You know the situation better, and as always, to have children or not is a choice for you and your SO, and being pressured in an ongoing manner is not acceptable.