AITA for telling my sister she has unrealistic expectations regarding her daughter’s name?

My sister, Lauren, has a 3 year old daughter. My niece has a name that can be easily shortened. It’s not this, but think Emmy for Emily or Katie for Kate. That sort of thing.

Lauren has requested that family not shorten her name as she doesn’t like any versions of that. I thought it was reasonable and we all respected it.

Now…my niece is in preschool and naturally, the other kids are shortening her name. Lauren went to the teacher and said something, who said she can’t control something like that.

Lauren was ranting. I pointed out that she can’t control this for her daughter’s whole life. Not to mention what if she prefers that nickname as she grows up?

Lauren said no. It’s not much to expect people correct their kids, students, etc. I told her she was being ridiculous. If she wasn’t prepared for all of the nicknames associated with the name, she never should’ve named her that.

My sister is now accusing me of trying to tell her how to parent. Some family thinks I should’ve stayed out of it. AITA?