Theory after the finale
The show has me so confused and my theories change like every day but after the finale I changed it again and want to know what you think.
I think the person who visited Mona in the red coat was Melissa. It's been shown in a few episodes that she has a red coat just like it. And I don't think Mona respects or cares for Spencer at all. I think Melissa wanted to give Spencer the chance to be part of the -A Team because even though they've had their differences, she still cares about her younger sister and wants her to be protected. But she made Mona do it because she couldn't risk being found out if Spencer rejected the offer and told people about the things she's done, like the police even. "I did everything you told me to." I think Mona meant everything she did with Spencer in that episode. And I know, I know, Melissa is way too obvious, but that's clearly the direction they're going for since Mona turned out to be such a big part of -A. Oh, and remember Melissa and the toffee ice-cream? Mona said something about toffee lipstick. I really think Melissa and Mona are connected.
Or it could be Aria because the toffee thing involved her too but that whole thing isn't very significant. I think she's closer to Spencer than the others though and she may have wanted to protect her if Spencer wasn't very important to the main -A. There's lot of Ezra theories and a lot make lots of sense, so I think Aria may have joined if he was a member. But then that would only leave Emily and Hanna to be victimized which I can't find a reason for. But they are the two who have gotten the worst of -A's treatment. Marlene King said Aria's outfit was very significant in the finale. If you look closely, the gloves she's wearing look just like -A's. Also -A was supposed to be 'unmasked' in the finale and when Ezra and Aria kissed, they literally 'unmasked.'
So, what do you think?