MIL wants my baby to call me MAMA

Does any of your MIL (chinese) likes to call herself Mama to your baby? Typically for chinese the grandmother at father side is called Ah Mah. But she double the last word to make it sound Mama. I have been very uncomfortable with it and have voiced out my frustration to my hubby. But he dismissed it as he thought its just a small and stingy issue. I also couldn't possibly say it in her face to say Stop asking baby to call u Mama as I don't dare. Somemore she is taking care of my baby 24/7 hence I'm scared that my baby really call her mama next time. What should I do?