If the climax is when they find her body in her house, what is the falling action?what is the falling action after the climax?

Actually, the climax is not when they find a body in her house. Most readers have figured out from various clues, that Emily had already killed Homer. She had bought arsenic, Homer disappears without a trace and the smell ( probably that of Homer's body) lingers around her home. In addition, her servant, afraid of what they will find, leaves the house immediately after the townspeople enter. The climax of the story is in the last line. As pmiranda points out:

Then we noticed that in the second pillow was the indentation of a head. One of us lifted something from it, and leaning forward, that faint and invisible dust dry and acrid in the nostrils, we saw a long strand of iron-gray hair." (Faulkner)

This is the final line of the story and the climax. The horror of discovering that Emily had been sleeping with Homer's dead body is the high point of the story. The shock leaves no need for falling action.