Mother in Law problem

So, I just need to vent for a moment.. if this is an inappropriate place to post this, I’ll delete it. We found out the 18th that I’m pregnant for the first time and decided to get married the 20th (we were already planning a wedding for May anyway, which is still going to happen). Although the fact that we weren’t married yet wasn’t “ideal” we’re thrilled! We told my parents (also thrilled, but wanted us to go ahead and get married) and then decided to tell his mom, who is a little.... unpredictable. She wasn’t nearly as unhappy/upset as we expected but I definitely wouldn’t say she was thrilled. We were trying to find a special way to tell his grandparents about their first great grandchild, when his mom decided to ruin the surprise. She hasn’t explained herself yet and I’m really really hoping that this wasn’t intention... but I just don’t know. I was mad at first but now I’m just heartbroken because it was important to me to tell them in a special way and I don’t know if they’re mad because of our situation. I just don’t understand why people have to be so untrustworthy...