Well. Considering how they bothered to show that little segment of her resolve about death this episode, I think she is a character significant enough that they wouldn't just let her go like that without having her identity revealed to the protagonists.
And while the helmet was partially broken, it might not have been enough for the transformation to wear off. After all, her initial transformation scene in episode 5 seemed to imply that it wasn't just the act of putting the helmet on that caused the transformation to occur, but some kind of a spike underneath the helmet stabbing her head and having power inserted through it did.
Not to mention that there's this illustration from the light novel as well:
