The A.D. initials are the clue. Bethany Young is AD. There are similarities between Agatha Christie's Evil Under The Sun and PLL. There are chances that real Alison Dilaurentis was actually killed on that night. The one living as Ali is Bethany Young. But more than that it is interesting to unfold my theory about why Aria is not tortured as much as the other girls. Also, why did A.D. tell Aria that she looked good in a black hoodie and that her relationship with him/her was not over? My theory is that A.D. is Aria's sister Bethany Young. She is also Toby Cavanaugh's and Wren Kingston's sister or love interest or close friend. Let me tell you how. She might be Marion's daughter which makes her Jenna's step-sister. Or she can also be Mary's daughter and friend of Jenna probably she was also in Radley. Wren Kingston is Bethany Young's brother/lover. She is the daughter of Marion/Mary and Scott Montgomery, She has blonde hair and looks like Aria/Spencer. That is why Aria resembles her so much. She was working with Ezra who was sponsoring her antiques. Ezra may have actually fallen in love with Aria but is afraid to confront AD.
Why Torture Liars?
The truth is likely that Charlotte hated Alison. She secretly conspired against her and joined hands with Bethany Young and the entire NAT club. On the day of Jenna Thing, Bethany's face was injured. She decided to kill Alison. The NAT club and Charlotte conspired in the entire event but Alison was either killed and Bethany was removed or Alison fooled the NAT club and Charlotte in believing that she was actually Bethany. So, why did this confusion happen? The two reasons are that they were wearing the same clothes and same looks. Bethany had disguised herself as Ali and so, Mrs.D protected her. Or Mrs.D actually protected Alison who wanted to get to the root of who was trying to kill her. But she participated in the game and joined in. Charlotte was also playing the game and trying to confuse Alison.
It is possible that Alison had actually killed Marion and Bethany would have been made the scapegoat. This and the Jenna thing angered her. Charlotte was the link between Bethany and Alison. She was also working for Ezra at the same time. However, after going to radley which she went to cover up Bethany Young, she didn't want to start the game again.
Mona was in touch with Charlotte because she was working for A or A.D. Through her conversations, she had understood that Charlotte just wanted a way out and a life with Rollins. But this angered Bethany who devised a master plan to get her out of Radley and then get her killed by Mona. Yes, Mona is lying to the girls. She is still working for A,D.
Then Uber A wanted liars to take the blame for Charlotte's death because that would make them suffer. She wanted to Mona to stay out to continue the game.
Uber A either looks like Spencer or Aria, it is also a rare possibility that she looks like Alison. In either case, she is a blonde. But she is Wren's sister/lover and he will kill her in the end. May be Mary Drake is actually saving Uber A and not Spencer. Aria was probably in Radley and was friends with Bethany Young who is her cousin.
That is why, Bethany doesn't want to break up Ezria. She is also soft on Emison because, she is not entirely hateful towards Emily. It is Wren who wanted to torture Hanna because she rejected his affections. It is also likely that Wren is not Bethany's brother but her boyfriend or a friend. This is especially true since, he has been Spencer's boyfriend or lover although it was disgusting.