I am not sure whether this functions as a nightgown or a chemise or both.
Here's a pretty good view of the sleeves and the fabric.This is a shot of the front.
Pull up your neckline, girl!
I am not sure, but I wonder if Simplicity 9769 (Misses Civil War Drawers, Chemise, and Corset-- View A) might work to make a chemise that is similar, though not exact. I am sure there are many other patterns that might resemble this one that Cynthia wears.