Yeah, i kind know now but thanks :)
I think that a twin would be surprising if it was a different person's twin. What if Aria had the twin and Maybe Ella and Byron didn't want two kids at the time and gave her away on purpose and she found out and was mad at Byron and Ella for not remembering her and became A to get revenge on them by torturing their kid who she probably thought they liked better (because they kept her instead of her twin), but knew she couldn't without torturing all of them or else would be suspected.
I think that in the show Alison(or Courtney) have/had a twin sister because they are many clues, like in the Halloween episode of the season 3 : the little blond who dissapear, and in the season 4, the two little blond in red coats! There is many clues too in Ravenswood the spin-off!! With the little dead blond!
(Sorry for my bad english, I'm french)
P.S.: There is many clues with the twins and the France too!!!
Hey Don't say that it's because when Sara and Marlene said that the a is for answers will be the the same story as the book