We're leaning toward the former, but we could easily see it going in either direction. We've broken down why we think she may be part of the evil gang — and why she very well might not be, too.
Why she might be part of the "A" team: Well, she's crazy enough, that's for sure. Also, at this point all of the "A" members seem to be people who hated Alison (Sasha Pieterse). Meredith could easily fit into that category, because of Ali's blackmailing ways. (We even think it's plausible that she was involved in Ali's death.)
More generally, there's also the fact that Meredith got involved Byron (Chad Lowe) again, and intentionally applied for a gig at Rosewood High. What better way to help the "A" cause than to first get close to Aria's (Lucy Hale) family, and then get a job at the school where so many of "A"'s plans go down?
Why she might not be part of the "A" team: Sure, Mona (Janel Parrish) went off the deep end around the end of Season 2, but for the most part the "A" team is full of cool, collected schemers who don't just snap and reveal the depths of their crazy at the least sign of a problem. Meredith's over the top actions in Episode 16 make us think she's more likely independently crazy than part of the team.
What do you think: Is Meredith part of the "A" team, or is she operating on her own?