When you look at this painting (which is on the second floor in the hall that leads to the locked door), Nancy makes a comment about it being smudged.
What she really means is that the area to the left of Clara has been painted over to cover something up. You need to remove some of that paint --
-- and for that, you'll need some turpentine and something that can serve as a rag.
There's a large can of turpentine in the tool room, on the left as you enter.
As for a rag, it makes me wince to think of it, but you can use one of the napkins next to the tea service in the parlor. (Kids! Don't try this at home! Your mom will crucify you!)
Go back up to the painting of Clara and click on the napkin to bring it up into your window. Use the turpentine on it, and you now have a "cleaner-soaked napkin" in your inventory. Use this on the left side of the painting to reveal something odd.
Ask Clara about it, and she gets upset and refuses to talk about it. But you can now go to the cemetery --
-- and go up past the fountain on the right, then look at the weeds at the left. Clear away the weeds to see two small headstones.
You can now talk to everyone about the 54 souls. It's an interesting conversation.