Ok, I have another theory: it's an echo of Zenon.
We have evidence that the Watch is capable of implanting personality fragments or echos into the minds of those it is used on. In #878, Zenon says "The Watch's patterns are a part of me now", before he uses them on Erin to try to take control of her. Suppose this implanted an echo of Zenon into Erin's mind, and that it's still there even after her liberation from his direct control in #924. The final panel of #928 strongly implies that something is still wrong with Erin, although we haven't seen any obvious effects since then. But there may be an echo of Zenon inside Erin, perhaps suppressed or too weak to control her directly, biding its time.
Then Miriam comes along, sucks Erin's soul into herself and sets up a dream sequence empowered to brainwash her. If these sequences are partially generated by the subconscious of the victim, as the mermaid theme of Amaltheia's sequence suggests, that would give the Zenon echo a chance to influence the nature of Erin's sequence. The echo inserted itself into the dream in the role of "the doctor" and leveraged Miriam's power to take control of Erin. Now it is leveraging that power to pull Miriam herself into the dream in an attempt to take control of her as well.
That… actually makes quite a lot of sense, especially in tandem with something else I noticed earlier in this mess.
One thing I like about Mallory’s reprogramming is that it seems to be a direct inverse of what happens to her when she and Erin get caught by Zenon. Zenon, likely echoing Jakob in whatever strange way he is, is the one who turns Mallory into the wind-up fuckdoll, the “tits and holes.” Yes, Zenon gets defeated, but the Watch programming doesn’t just vanish. You can even see hints of this in 995 “Something Lingers” with Kanti, who seemed to have some residual effects from her time in the cloud.
Smash cut to Mallory immediately post-Zenon:
Adrian: are you okay?
Mallory: that is a more complex question than I can answer right now.
And later on, in 937:
Adrian: you’re sure you’re okay for now?
Mallory: yes, please help Dani.
It’s clear that Mallory has lingering trauma from what happened to her in the cloud, that whatever adjustments Zenon made to her Watch programming have aftershocks. Thus, when Jakob in her mind leans into the “tits and holes” talk and belittling her intelligence (Zenon: you’re only good for one thing… and you don’t need a brain for that), it follows that the new Watch is being used to purge the lingering effects of Zenon as well as Jakob.
The problem is, Erin has yet to be exposed to the new Watch. Everything in her mind, all the way back from the original Night of the Watch, is still there, and is now being tweaked by Miriam. Thus, whereas before her soul and her mind may have been able to suppress the influence Zenon left on her, now that they are divorced and Miriam is forcefully dunking her head under the water, Erin may be instinctively grabbing out to drag Miriam down with her.
Gosh, thinking about this, it seems so plausible and follows so well that now I’ll almost be upset if this
doesn’t end up being the case.
Edit: Adding this as an unrelated(?) note, but the hypertext for 928 reads ‘you’re the one who’s crazy’