I tried to set up a middle name for
Miriam beforehand - I wanted to call her
Merry Mae. It never worked. I've tried a few times to create a nickname for her - it hasn't stuck. I'm not sure why, as my family is really big into nicknames. But
Miriam is
Miriam.
I really don't care what people call my daughter. My mom refers to her as
Miriam Elizabeth, my brother calls her
Miriam Mae and we call her Miss
Mae when she's in trouble. I'm actually surprised that my family hasn't created a nickname for her - they have done this for all the other grandchildren.
As for your choices I'd go with Nin. It's cute, sweet and simple.