For the Muggles in the room, the Patronus charm conjures up a spirit animal that protects its witch or wizard from deadly Dementors. Just as the wand chooses the wizard, you can't control what creature your Patronus is. That's where Pottermore's quiz comes in: Fans go with their gut instinct, answering a series of timed questions. Lynch was displeased by her fishy results.
She even took the quiz twice, hoping to get a cat. (The first time, her Patronus was a Greyhound.) For the record, there are 14 known types of cat Patronuses, from ginger cats to Siberian cats to something called a polecat.
Or maybe a lion would do. There are two lion Patronouses in existence: one male, one female.
Sorry, Evanna, but there's no arguing with the official Patronus quiz. It's Rowling's wizarding world and you just live in it.