Who is the real A from pretty little lairs?

Ali. Ali has a identical twin sister named Kourtney. We have never heard about her because she was in the hospital for being mentally ill (crazy). Ali was sent to the hospital by accident and the "Ali" the girls knew was really Kourtney. Ali managed to escape from the hospital and get revenge on Kourtney by digging a hole, pushing Kourtney in there, burrying her alive, pouring concrete, more dirt then some grass over it. This was all for revenge. Ali then got ahold of Kourtney's diary and that's how she contacted the girls.