MIL baby name issue! Help!

One day when we visited his parents baby names came up and I mentioned how we had decided on that name, my mother in law was like mmmm no I don't like it and suggested we keep looking! To that I said no! His name is Maddox and that was that. So about a week or so later we visit and she mentions that she's going to nickname the baby "Ducky" because of Ma"ducks" she says! I was totally thrown off guard and shocked that she would nickname my baby before he was even born! Now I'm furious about it! I feel like she's trying to take my happiness away, like she wants to put her stamp on my baby! Am I over reacting about the nickname? She said her and her older grand daughters came up with it! So i feel like she's deciding what her side of the family calls him.