Board Thread:Manga/@comment-24680843-20171225223017/@comment-5179916-20180220043130

At first, I thought that being in the crystal would have stalled Annie from aging and progressing through the 13 years of life she had left and would reactivate after she wakes up again (similar to cryostasis) since there was no indication she had the same number of years left as Reiner. Now that Ms. Tybur has been seen using it, however, it seems doubtful that would have worked and Annie only has two years left as well.

If or when Annie comes back into the story (really hoping for the 'when' option), I imagine that she will have to really convince the 104th, and humanity as a whole, that she is truly on their side and not Marley's. Sure she was sent to destroy the 'Devils of Paradis' but she was not fully commited to it like Reiner and, to an extent, Bertolt were. She just wanted to have a normal life and reunite with her father again and this would have been the quickest and easiest way to do it. I believe Eren knows this due to his interactions with Reiner but everyone else will need convincing, especially Mikasa, who will no doubt try to kill Annie the minute she sees her.