For anyone looking for a prompt to do this manually, it seems to be as simple as this:
> Generate a version of this photo that can be used as a coloring sheet
> Generate a version of this photo that can be used as a coloring sheet
> Make this a page in a colouring book. The drawing is in a simple Studio Ghibli portrait style. Bleed all the way to the edges. Background colour is #ffffff and lines are bold and #000000. There is no shading or crossthatching.