Too good for general tween public?

DD, as it turned out at the end of the school year (something that deserves a post of its own) has been having social issues at school.  To this day not really sure what issues she is having (again, post of its own), but I think I have a clue or two.  My guess was proved right by the conversation we had today.

DD:  T told me today that I am a nicee.  Mommy, what is a nicee?

SW:  No clue.  

DD:  Well, she said I am a nicee, and she liked normal people.  

SW:  Did she explain what she meant by that?

DD:  She said I am too nice all the time.  Is that a "nicee"?

SW:  I don't know.  Maybe she meant she doesn't like people who fake being nice?

DD:  No, she said I am too nice.

SW:  So basically she said that she wanted you to be meaner to her.

DD:  ...

SW:  Did you tell her to @#$$ !@#$ !@#$?  (Okay that part was an imaginary scenario of what I quite possibly would've said in real life to any adult accusing me of being too nice to him.)

I am greatly bothered by this issue and not only because DD is involved.  I don't get it.  I really, really, totally don't get it.  Why does being nice to peers results in social awkwardness?  I know DD is not one of those who is faking niceness (not sure whether 7 year olds are even capable of that).  She is a genuinely nice and considerate kid, and quite honestly I had very little to do with that.  She was just born that way.  So why are kids so nasty to each other?  Why are bitchy girls more popular?  Now in my olden age, when I have acquired some experience and wisdom - hopefully, I see how rare are people who are genuinely nice and take time to be considerate.  Those are the qualities to be cherished, and people exhibiting them should be treasured.  So I don't get the younger kids who not only  don't value niceness, but actually consider it a vice.  I guess that means that I don't get my younger self.  It's hard to describe how much I want to go back in time and slap her around, for her own good.