We already know that Mrs DiLaurentis had an affair with Spencer’s father (Peter Hastings) and produced Jason DiLaurentis, but what’s not said is that Mrs DiLaurentis actually had twins; Jason DiLaurentis and a girl Bethany Young. Bethany was a 17 year old patient at Radley Sanitarium the night Ali went missing- the same age as Jason. In the episode ‘Taking This One to the Grave’ Spencer finds a tape in which Bethany talks about Mrs DiLaurentis and they discover that she was having an affair with Bethany’s father (Peter Hastings.)
On the night of Ali’s death, Bethany escaped Radley following Alison’s invitation, to come and visit her on Labour Day weekend. In the episode ‘How the ‘A’ Stole Christmas’ Hanna finds a letter in Ali’s attic in which Bethany writes how excited she is to go and see Alison on Labour Day Weekend and thanks her for sending her clothes, saying that yellow is her favourite colour. Now think back to what Ali was wearing on the night she went missing: a yellow blouse.
On the night Ali went missing, Ali walks into her house to hear her mother on the phone saying ‘how could this happen? I don’t understand.’ She then looks nervously around the garden as if she’s expecting someone to turn up there. The phone call was from Radley, explaining to Mrs DiLaurentis that Bethany has escaped. Something they would only do if Mrs DiLaurentis was Bethany’s next of kin. Mrs DiLaurentis then forbids Ali to go out and says to Radley on the phone ‘you have to send somebody, immediately’ and that she is ‘very very worried.’ Earlier that day whilst Alison was visiting/threatening Jenna in hospital, she received a text saying ‘Bitch can’t see you but I do. Tonight’s the night I kill you. — A’ now at this point it’s important to remember two things;
1.) Ali loves changing identities. Her and Cece would frequently pretend to be one another, and let’s not forget Vivian Darkbloom.
2.) Bethany and Ali are part of the same family, and are bound to think in the same way. We already know Bethany has mental health problems as she is in Radley to begin with and Ali’s way of thinking is also pretty twisted, centering her lies around games and trickery.
Once Ali received the text, she makes a plan to trick whoever A is into mistaking Bethany for her. This could either be because she wants to secretly watch as A approaches the wrong girl, therefore exposing his/her identity or because she is genuinely worried A is going to kill her and would rather Bethany took her place. What she doesn’t realise is that Bethany has other reasons to visit Ali. She is jealous of her. Mrs DiLaurentis was conveniently on the board at Radley when Bethany was a patient and would take her out on day trips. On one trip to the stables, Mrs DiLaurentis asks Bethany to call her aunt Jessie, which angers Bethany (which is fair enough as she is actually her daughter) and causes her to call Mrs DiLaurentis a liar. Why is Ali accepted as her daughter and she isn’t? In Bethany’s opinion Ali is just as twisted as she is and as Mrs DiLaurentis said ‘you can never turn your back on a Hastings.’
On the night Ali goes missing, both girls look identical to each other (this is done on purpose) and Ali makes sure that people eg. Ezra and Ian see her. As A is always watching, A is very likely to have seen her too and know what she is wearing. As Ian is walking away from seeing her at the kissing rock Ali says ‘I’m just killing time while I wait for someone better (Bethany) to come along.’ Ali returns to the barn where all the girls are asleep. As she is walking home, Bethany creeps up behind her and hits her over the head with a rock, whilst Mrs DiLaurentis watched. Ali’s mum burys Ali saying ‘what have you done, what have you done!’ the whole time. We know that Mrs Grunwald then pulled Ali out of her grave after she had been buried, saving her life.
Now I personally think that after these events, A (mistaking Bethany for Alison in the yellow blouse) hit Bethany over the head with a shovel. At which point Melissa buried her. This would make A responsible for the death of Bethany Toung and explain why Mona was killed; she was getting too close to the truth. (Although there is the possibility that Ali herself hit Bethany with the shovel once she had been saved although I doubt that is true.) I haven’t gone into detail about who A is otherwise this post will become twice as long, but this Bethany theory definitely matches up to all the clues the pll writers have given us