I like it, I'm a fan of the Harry has a twin sister stories. I would like to see the Dursleys yelled at a bit more because otherwise they get off with less than from Hagrid who scared the crap out of them and gave Dudley a pig tail.
Author's response
McGonagall's pretty imposing even without the pigs tail--though I'm not saying that ickle Didders will never have an extra appendage... I'll probably revise it so McGonagall gets a bit more scolding time.
Thanks for the review!