MIL "won't" let me use cloth diapers.

My SO and I want to use cloth diapers for very good reasons. This was brought up in conversation. And my MIL just quickly turns and snaps "no you won't." without any further explanation. I replied "yes we will" and her response was "I'm not going to let you. I didn't do that for my kids, you won't do that to yours. End of discussion"

Who does she think she is?!