You weren't being selfish, unless your choice somehow prevented someone else from having children. In fact, not allowing your genes to compete for resources is actually quite charitable. You're limiting the number of people that will use up a diminishing pool of resources and thus, slightly improving the quality of your life and the lives of those around you. What she should have said was, "Bah, more room for mine then." or something along those lines. Saying that you're being selfish, while understandable(she probably thinks you don't want to share your resources with a child), isn't completely justified.