TAKE X/The Centrality - Discussion

The answer is sort of a combination of the two.

The Ammon acted as Sienna's eyes and ears in the Normal Place. It had its own autonomy, but it basically was just doing what Sienna wanted (and in fact was almost just an extension of her - Sienna marked it as a hero and in doing so imprinted a lot of herself on it). When the final case rolled around and Sienna started taking a more active role, she decided that the Ammon wasn't serving its purpose anymore and disabled it.

Think of the Ammon as a mini Sienna drone, or something like that, basically.