Ok so I have a theory it's a bit crazy but here it is. I don't know if you know of the 1960's movie 'psycho' but its made by Hitchcock, who's movies Marlene king bases some of the episodes on.
Rest of the message: In the movie psycho the killer in the end turns out to be the main character Norman. When he killed someone he was dressed as his mother who died, as he had a split personality. I have a theory that maybe Aria is A and has a split personality and when she is with the liars she is Aria but when she is alone or in the A lair she thinks she is Ali.
OMG who thats a great theory! Love it! x