Shocking MIL issue - opinions please

Krista
My mother in law, after a 3 week stay, has today told me that when she drove alone with her 3 kids in the back seat, she would carry a riding whip and smack them with it while she was driving if they didn't behave. She also told me she threatened my husband when he was little that if he didn't behave in the car she would pull over and leave him behind. SHE DID THIS. She said he was bad so she stopped at a gas station or rest stop, LEFT HIM, drove half a mile then came back for him. 
She has said other things that sound benign but I would never do - like I should let my then 5 week old cry it out, that I should put him to sleep on his belly, and she - a smoker - put her nasty dirty finger from her nasty dirty smoking hand in my son's mouth!!
I never, ever want to leave my son alone with her. Ever. My husband has never told me these stories, I don't know if he remembers, but I want him to know how I feel about this and why. Do I tell him and risk him finding out things he didn't remember? Do I just wait to see if it ever comes up? His parents live in Europe so we likely won't see them again for a while (maybe in a year). I am just so furious and am glad she waited till the day she's leaving to tell me these things. I want her out of my house!!! 😡