I'd really like to see ideas like this in fan fiction.
There's sufficient level of details and background which can really fit in too.
Alice wants to have a doll which gains life, Narumi would be able to also explain the differences and the details between "life", "animation", and "life force".
This also allows Narumi to explain why she's able to nullify fairies who are life force and her ability more in depth.
She's a youkai of an inanimate object, similar to Medicine, but both are not tsukumogami. (Compare to Hata no Kokoro, who is a menreiki, which is a form of tsukomogami.)
Another one would be a somewhat mischievous or fun loving Narumi either striking back at Marisa as a payback for one of her antics or something, and that in the form of giving life to suspicious and interesting shrooms that the black and white magician would usually collect ; or actually turning out to be one of the reasons why the forest of magic's got lively monster shrooms and plants ...
I'm reminded of Marisa x Alice fan works, where Alice has a mini Marisa doll...
Alice makes the doll, but leaves it on her work bench. (Narumi and her would be close friends.)
Remembering the part of where she hears Alice wanting a living doll, she gives a little bit of life to it and suddenly we have Mini-Mari.
Now a new incident of where books and items are getting stolen left and right, even though Marisa claims she hasn't stolen them.
Hong Meiling: "How could she steal any books?, she was in front of me the entire time??".
Patchouli: "My library is getting robbed, but the suspects are missing!"
Reimu wonders if Marisa figured out a way to clone gaps or back doors...etc
Alice wonders if Marisa made a crazy potion or something, since now there seems to be two of her going around.