While you may want to take the spoilers on this Twitter account with a grain of salt (a.k.a., definitely do!) they do present quite a compelling theory. According to the account, Uber A is actually — dun dun duuuuun — Lauren DiLaurentis, a.k.a. Alison's (Sasha Pieterse) secret twin. Alison doesn't actually have a twin on the show (at least, not yet) but the alleged "spoilers" tie her into the story quite nicely.
According to the Twitter account, Lauren was the twin whom Charlotte "tried to drown" in the bathtub. She lost her sight during the accident and was sent to a school for the blind — the same place where the Liars were nearly murdered at the end of season 7A. Lauren used the guilt that Charlotte had to control her in order to torture Alison, whom she hated.
"Lauren and Jessica used the guilt Charlotte had of the mistake she made as a kid (blinding and burning Lauren in the tub) to control her."
The account also states that Lauren befriended Jenna (Tammin Sursok) and Lucas (Brendan Robinson) and recruited them to her side. Lucas was apparently in love with Charlotte, and was working to take down the girls in order to learn of Charlotte's killer. That certainly gives credence to the theory that Uber A and A-Moji weren't the same person: Lucas would have been the one sending those bizarre emoticons, while Uber A (a.k.a. Lauren) was doing the heavy lifting.
Other random spoilers from this account? According to @PLLInsider, Pastor Ted (Edward Kerr) is Charlotte's biological father (called it) and that Mona (Janel Parrish) dies trying to save the Liars from a fire — a fire that is also a big part of the PLL book series.
So... how accurate are these spoilers? I'm a total skeptic. I think it's far more likely that these tweets came from a clever fan than anyone actually associated with the show — but that doesn't mean what this fan is saying is totally false. Fans have long suspected that Alison has a twin (she has one in Sara Shephard's novels) and many people believe that the ever-sketchy Lucas is a part of the PLL endgame. This Twitter account may be fibbing about their authority, but they're not necessarily taking shots in the dark here.
Alas, we'll have to wait until the show's series finale to find out if there's any truth in these tweets.