Mil told stepson grandma is dying

So my mil told my 6 year old stepson his grandma is dying (she has terminal cancer) and is very sick in the hospital. She then blamed it on my husband saying he’d already had the conversation with stepson and she was comforting stepson. It’s rubbish we have not told stepson what is going on as we are in the process of getting therapy set up so that he has a safe place to express his emotions when she does inevitably die. My husband has called stepsons mum to ask her if she gave permission for his mum to have this conversation and she was also confused and said she didn’t give permission. We as a family have been no contact with mil for about 6 months now and I know she’s blocked on my husbands phone so there is no way he could have said to her it was okay to have this conversation. Stepson is now distraught and has so many questions neither me or my husband have the answers too. To say I’m angry at her is a complete understatement. How the hell did she think that’s a acceptable conversation for her to be having with no therapy set up or no parent agreeing to it 😡