To make matters worse, her husband didn’t even stand up for her. 

If you’re constantly getting berated, put down, or yelled at, there’s only so much you can take before you snap. You might have been that kid in school who kept getting teased, and when you finally snapped and told your tormentor to knock it off, you got in trouble for raising your voice or being too aggro. It’s so frustrating to be in the position where you’re being treated like you’re overreacting when everyone around you is blissfully unaware of how much you’ve had to endure at the hands of others. Browbeaters can be extremely subtle about their cruelty. To the outside world, it might appear as if they’re not doing anything at all, which is why they freak out when their victims stand up for themselves. 

When you’re getting tormented, it’s important to have someone in your corner who is willing to stand up for you. If your mom wasn’t the kind of mom who would tell the principal exactly what was going on with you and your tormentor, then I feel sorry for you. If your romantic partner is not willing to stand up for you against your cruel mother-in-law, you didn’t choose a good one. Anyone who expects you to merely tolerate cruel insults does not love you enough. They care more about maintaining the peace than justice for the person they should love.