Because she was locked up and crazy and wanted to be her and live a normal popular life
Courtney Alisons twin sister
She doesnt but if she did it would be to throw the pretty little liars off.
Yes
No. Courtney is dead
In the show they say nothing about Courtney but in the series they are identical twins.
Because she was usually in a mental hospital.
If you are referring to Courtney from the Pretty Little Liars book series by Sara Shepard, it is unknown if it will be on the series. What I do happen to know is that we will find out who "-A" is at the end of Season 2. I found this out on the website, abcfamily.com and go to the Pretty Little Liars blog. As you know, Courtney was in the books, and honestly I hope she's on tv. That would be a great twist. Hope this helps a little, considering it's the best to anyone's knowledge at the moment.
Courtney
She stole Ali's (Courtney's) diary.
In the books, Jason DiLaurentis does know. He is closest to Courtney out of the twins
Courtney is alison's twin sister, who pretended to be her
You find out about Courtney in the book Wanted.