What is the name of the twin-like sister of Roderick Usher in Poe's story?

The twin-like sister of Roderick Usher in Poe’s story is Madeline Usher.

Madeline is one of the last two surviving members of the Usher family, along with her brother Roderick. When the unnamed narrator arrives at the decaying Usher mansion, Roderick explains that Madeline suffers from mysterious illnesses and episodes resembling cataleptic, deathlike trances. Her condition contributes to the story’s atmosphere of uncertainty: the characters and reader cannot always tell whether she is truly dead.

Roderick eventually tells the narrator that Madeline has died. The two men place her body in a family vault, but the decision proves disastrous. Madeline was not actually dead, and she later escapes or breaks out of the tomb. She returns to the house at the climax, terrifying Roderick and revealing the destructive bond between the twins.

“The Fall of the House of Usher” first appeared in Burton’s Gentleman’s Magazine in September 1839. Madeline’s name is sometimes confused with Poe’s recurring figures such as Lenore, but Lenore belongs to “The Raven” and other poems, not this story.