Harper will take care of that, but you have to approach via the secret passage.

Remember what happened when you solved the clocks in Charlotte's bedroom?

How do I set the clocks in Charlotte's bedroom?

Go through the painting in Charlotte's bedroom to reach a spot behind one of the parlor walls. Wait till you get the message "Clara leaves." Then it's safe to open the door and go in.

But be quick, because she won't stay gone forever.