Maybe I'm tripping, but I feel like moms of boys are usually a little weird. Maybe it's just because it's not a dynamic I relate to, but moms who are super possessive of their sons always freak me out. I get being protective, but sometimes it's too far. I don't wanna get Freudian, but there are too many stories like this to ignore. And it usually comes out the strongest when their sons get married off. Then the moms struggle with letting them go, and the brides usually get the brunt of it. They quickly become the other woman competing for her son's attention, and it rarely ends well. It, unfortunately, is a tale as old as time.
But what makes this story so satisfying is how perfectly the couple dealt with this overstepping mom. This Reddit story should be disseminated to everyone in this situation to show them how best to handle a monster-in-law.