The way I saw it, it wasn't so much a part of her brain, as total brain activity, like an energy field. Like spare cycles on a CPU – if you're not using them to crunch data yourself, you can donate them to the render farm or search for extraterrestrial life or fold proteins. It's still more sci-fi than fantasy but in a different way.

I very much like your book interpretation of the fic. Yes, Prof. X, everyone is much safer with a Matilda operating at peak mental capacity.