Why it's possible:
- Listen, Mona's crazy. Always has been, always will be. We've come to realize she was insane long before she took over as "A" and long before her stint at Radley.
- She's already been revealed as a member of the "A" team, and she could still be on it. Plus, she knew Ali was alive this whole time, so she'd surely have the upper hand.
- Let's not forget that weird scene with Wren, where she talks about loyalty and secrets.
Why it's not:
- We've seen Mona cross over to the good side already. Plus, she says someone took the game from her while she was in Radley.
- Mona's been put in clear danger by "A" before (like during the lodge fire).
- She didn't know who Red Coat was.
Source: ABC Family