I hope she's not a real school girl who got lost and ended up in Comiket or something like that.
She actually reminds me of Chibi Usa from Sailor Moon. I think she first appeared in the second season and she attended school during that time. This can’t be her though, because Chibi Usa’s hair is pink!
Anyone know what series she’s from? Thanks to Pitaten for sending this!
EDIT: Thanks to kawainu for letting me know she's Hachikuji Mayoi from Bakemonogatari!