Julie's right - all MILs are slightly cooky

. But, yours needs to be put in her place. Good for you for telling her off! How, it's your DH's turn.
Any issues I have with my MIL I sic DH on her. He won't hesitate to tell her she's wrong and to mind her own f****g business. She's a good woman and not a bad MIL in general, but she has some depression issues that creep in a make her say cooky things that she wouldn't normally say. I can fight with her all day long, but she backs down to DH, and I think it's because she realizes that he will always be on my side, even if I'm wrong.