MIL vents are one thing, this is an issue of safety and protecting your family. That's not unreasonable in my eyes.
Is there anyone that can go and log into her account and fix her settings? Or maybe she can give you her password and you can fix them? Sounds like getting those settings fixed would be the easiest route, though it's irritating when she doesn't just ask or listen when you tell her not to post pictures :P When DD was born I stopped just short of a signed affidavit promising that MIL wouldn't post about the birth before I had a chance to. And this is an issue of your/your family's safety so it's completely understandable. Hopefully it gets figured out!