Over-excited MIL

My husband and I have known our unborn's gender for the past two weeks and decided to throw a gender reveal shindig with close family and friends. All went well until not even five minutes later after the big reveal, my wonderful yet trigger-happy MIL decided to text EVERYBODY who couldn't make the party the reveal results. My husband and I didn't know she did that until we tried to FaceTime my husband's uncle in Florida to personally deliver the news, and to much our dismay, he told us that he already knew via the text my MIL sent. I wasn't necessarily angry as much as I was annoyed since I didn't consider it her news to give, but it wasn't a big enough deal for me to hold on to my slight annoyed emotions. For the next twenty minutes or so, she threw herself a pity party about how bad she feels even after both my husband and I told her that she shouldn't beat herself up over it. 
I get it. She's excited and her elation over the reveal got in the way, but I felt like she kind of rained on our parade due to her text and subsequent pity party. 😑