In the end, I actually really liked the movie and think it was better off NOT showing the makeup.
I sculpted at least three or four variations on the design before it was approved, which began as a more aggressive, monstery look and was revised to be a bit more subtle in the end.
Kudos to the director for sticking to her guns on that one.
Considering her pregnant state and emotional arc thru the movie, the producers felt Sandra’s nightmare would have something to do with a twisted, demonic baby creature attacking her (that’s as much as I could gather about the context of the scene anyway).