T.G.
my daughter whom is now 13 went through puberty at the ripe young age of 9. She started with the dropping of grades, the mood swings and being mean to her siblings. Although she still does a lot of those things it has slowed down to a tolerable stance. It will pass, but my advice to you is only let it go so far because she doesn't know what it is she is going through. But make sure you don't let her go too far. I have five kids so I deal with a lot of personalities on a daily basis and I am surely the QUEEN of my castle. But be patient, she find her way in dealing with it. I too started at an early age.