My mother-in-law slaps me for addressing my 7-year-older husband informally

I have been married for two years and recently had a baby. My husband and I have known each other for 10 years, so sometimes we treat each other like confidants. Because my husband is easygoing and affectionate, even though he is seven years older than me, I am used to calling him by his name instead of using the more formal terms.

We live with my mother-in-law. When she is not around, I call my husband by his name, but when she is present, I try to be more careful. However, this only lasted for a while, as over time, I would forget and call my husband by his name again, since I feel awkward otherwise.

That’s just how I feel, but my mother-in-law sees it differently. She thinks I am being disrespectful by not addressing my husband properly. When we first got married, my mother-in-law gently reminded me about it, but I never managed to change.

A few days ago, I asked my husband to change our baby’s diaper because I was busy in the kitchen, and I accidentally called him by his name. At that moment, my mother-in-law was standing nearby and suddenly slapped me hard. She caused a scene, accusing me of deliberately going against her wishes and saying I wasn’t properly raised. She threatened that if I "accidentally forget" to address my husband formally one more time, she wouldn’t accept me as her daughter-in-law.

I’m taking care of our small child, yet my mother-in-law shows no mercy, and my husband didn’t dare to defend me either. When we got back to our room, he tried to comfort me, saying I should make an effort to change because we are living in his mother’s house, and arguing with her would only make things worse. He suggested that I apologize to his mother, but I think it’s my mother-in-law who should apologize to me because she was violent towards me.

This incident has left me devastated, affecting even my milk supply for my baby. I’m disheartened because my good intentions are misunderstood by my mother-in-law, leading to her hating me.

What should I do to prevent my mother-in-law from interfering in our private life?