Help help helpppp

Hey ladies I need an opinion.

So I posted a video of my son, and my baby’s dad commented a nickname towards my son that i repeatedly told her to stop.

I told her no, that’s not his name. And she commented

“An aunty has the right to call her nephew anything she wants, so yes for me.”’

Then she proceeded to text my fiancé and said

“Tell your fiancé that no disrespect but i can call him whatever I want. Not even my own sisters say I can’t call them something”.

Again idk why im so annoyed but I was going to respond with

“Auntys don’t have rights to anything because they’re not the parents. So no, no it’s not. I would like you to respect the decisions we made for our son.

Thanks.”

Am I wrong for feeling so annoyed?

My fiancé didn’t defend me ONCE AGAIN and he says It’s not a big deal.

I’ve always truly hated her because she thinks she’s the boss of everyone. She’s only 4.5 years older than.