1. That she's a liar.
2. That in this particular scene we can take her at her word.
... often the same people. So I talked a bit about why can't both be true. I also talked about why I think she's lying in this scene, just like she usually does and why that makes more sense than accepting her statements to Sherlock there. So basically, on top of the "Is Mary a Liar?" question, this is me giving my reading of what's going on in that exchange between Sherlock and Mary.
(Do I still need to be vague to avoid spoilers? Has enough time passed that I can trust anyone who is going to see this show has seen it? There are major spoilers in this post, though I've tried to avoid them in this spoiler.)
(ETA: If you want to discuss this feel free to comment here. Or reblog/PM me there. Whatever works best for you.)