She's from Umineko no Naku Koro ni. Her name is Gapp. I personally find it to be a terrible anime since all it's always PEOPLE DIE, THEN THEY COME BACK TO LIFE, THEN THEY DIE AGAIN - IT'S MAAAAAGIC! But Gapp and her trolling ways is always lulzy.
"He who fights and runs away, lives to fight another day!"