Selfish

My mother in law asked yesterday when we were having a second because SHE thinks my son would benefit from having a sibling. I told her we weren’t really planning on having another. She get all bent out of shape over it. She told me that it was selfish of us and is mad at us....lol. Now she has me second guessing our decision. It’s making me feel bad and like I’m depriving my child of something. Is it selfish of me not wanting to give my baby a sibling?