What is this je ne se quoi?

Anonymous
I'm trying to describe this girl, but she has these multiple personalities. So I'm trying to describe to each one what I think of her, but I keep coming to the roadblock of "She is" but don't know what comes next. I don't know the word and I don't know how to describe the word. What does this mean? I'm fond of her but not in love with her. She and I get along so well, and I will tear apart anyone limb by limb who hurts her. That's enough of my tangent though... What does this mean?
What is this je ne se quoi?
2 Opinion