The plate for this one comes from the fountain puzzle in the ruins.
The sketch and a hint about which coffin you need can be found on a column of the main house, which you'll find after you find Jess's camera in one of the hidden places --
-- more specifically, in the area behind the wine rack in the cellar.
Behind the Bottles
The text next to the sketch says "First of its kind across the bottom." The coffins in the bottom row are all the same, except --
-- the coffin in niche 10, the second one from the left, which has two handles.
As before, any way you arrange the pieces so they fit is right, but here's how I did it:
This coffin opens to yield the second half of Charlotte's bedroom key.