MIL ruined my announcement...

This is my first baby after two miscarriages. We found out this morning that I am pregnant, and we were only telling close family until after 12 weeks to make sure that it is a healthy pregnancy. Well, before I even finished telling MY parents, my mother in law posted it all over Facebook! I had to hurry up and do my cute announcement much sooner than I wanted because she just couldn’t respect my wishes to keep it a secret. 😔 My husband doesn’t mind because she’s so excited and that makes him happy. Am I overreacting or is this totally inappropriate behavior??