Minnu basically means a nice but talkative individual. Occassionally, she can be a pain in the ass and derives pleasure, especially sexual gratification, from inflicting pain or humiliation on others. She keeps secrets among close friends or even just to herself for deeper secrets without exposing the truth.
Look, it’s a Minnu! Minnusaurus.
Minnu: define #2
Someone who is mean and goes around bullying people by calling them old.
Old lady: How old are you?
Boy: 25 this year.
Old lady: That’s really old.
Boy: So rude! You must be Minnu!