She became lost in the madness.
It’s understandable to some extent, because I have a theory about what’s going on.
There are three factions that I can see:
1. Shifters Village | Reiner, Bertholdt, and Annie
2. The Survey Squad | Erwin, Levi, Eren, Mikasa, ect.
3. The Reiss Family | Lod Reiss, Anti-human Squad, and Grisha (Formally?)
Eren instinctively bit his hand when he needed to materialized a Titans body, even though on one told him.