Assuming you have placed the currupt bonecharm on the throne prior entering the painting, you are told to knock out Delilah. And you might think you will have to knock out all of her doubles around the void. But as some of you might know, this can be difficult if not impossible at times. However, fear not, as you do not have to even touch any of her doubles.
As soon as you enter the painting and are in the void, turn right and take the clear path through the stone people.
After you have done that, you should turn aound and look up at the stone mountain above the painting.
You should be able to take the obvious climbing route up there. Once up there you will be able to clearly see Delilah.
After you see her, knock he out straight away and presume with taking her body out of the painting.
Hoepfully this helped you, as I was very stuck with this part of the game.