What would you do?

Shandy • Wife. Mom. Photographer. Baby #5 due 10/3.
We are a combined family of 6. Me and my husband have been together for 8 years. He has a 13 year old, I have an 11 and 10 year old, and we have a 4 year old. We are expecting a baby in Oct. 
So anyways we have a beach trip planned in June and we are taking all the kids. My mother in law has been very annoying and asking what dates we are going bc she wants to go at the same time with her 4 teenagers. We finally decided to just tell her after she told the 4 year old that she really wanted to go to the beach with her 🙄. So yesterday she tells us "oh I didn't know "all" the kids were going. I just thought it was Trent and Piper(her blood grandkids). I don't want to go if all the kids are going".  
She better be glad she said this to my husband on the phone and not Infront of me bc I would have went off on her ass...but what would you do???