My mom did something, and now I'm upset!

I told my family 2 weeks ago that we were expecting and that we have t told my husbands family yet.  She saw my husbands uncle at a event and Blabbed the news to him.  He is my father in laws brother.  
Well long story short she told him we were expecting and how excited they were.  Now I'm not sure if my husbands dad knows or not we were planning on announcing this weekend to him.  
My moms response was I figured you had told him already.  
I'm upset!  I wanted to announce to his family , it isn't her place to do it!