I don't even think you needed to apologize. How many times are people with no children offended (and say nothing) by thoughtless people who accuse you of not having a "real family" if you have no kids....or not being a "whole woman" since you aren't a "mother". I know I've been accused of being "selfish" and "immature" for not wanting/having children....sometimes even by strangers! I don't think your friend realizes how offensive she is being to you. You just illustrated that to her and put it back in her face. I'm personally tired of being battered by the kid-crazy crowd.
Although, I agree, you could show her that you are a bigger person by making a gesture of apology...but make it clear that you will not tollerate having your core being assaulted and your very personal choices ridiculed for her amusement.
