But why has the "A" team decided to turn their focus to Aria? We won't know the truth until the winter season rolls around, but that doesn't mean we can't speculate about it! Here are our theories.
Her dad. In the Halloween episode, Garrett (Yani Gellman) revealed to Spencer (Troian Bellisario) that he'd seen Byron Montgomery (Chad Lowe) talking to Alison (Sasha Pieterse) the night she died. Soon later he shows up dead, inside the same box that was supposed to be Aria's grave. Coincidence? Quite possibly not. If Garrett was telling the truth, it's very possible that the "A" team wants to keep Byron's involvement in what happened to Ali a secret. If so, they may target Aria to keep her from prying into her dad's secrets (or to punish her for doing so.)
As punishment for stabbing one of them. Or maybe they were trying to kill Aria at Halloween because of her dad — or just to prove how serious they are — but decide to continue to persecute her as revenge for her screwdriver-stabbing of one of their members.
Because she's the one who finds out about Toby. We know one of the Liars will find out about Toby's (Keegan Allen) involvement with the "A" team in Season 3, Episode 16: "Misery Loves Company." As we've mentioned before, if Aria is the first to find out, the "A" team could target her to keep her quiet.
Ezra is part of the "A" team. We're just throwing this out there. Ezra is still an "A" suspect, and his randomly appearing on the train at the end of the Halloween episode didn't exactly make him seem less suspicious. If Ezra is part of the team, maybe he had been keeping Aria safe. If he then found out she was keeping a giant secret from him, maybe he got pissed and decide not to protect her anymore.
Why do you think "A" is targeting Aria now? Let us know in the comments below.