Army of Darkness

From a slave coffle, a brief flashback to Evil Dead II (which itself starts with a recap of The Evil Dead) explains the Necronomicon Ex Mortis and how Ash got to where he is, Ash (Bruce Campbell) lands in Medieval England, where he is immediately captured by Lord Arthur (Marcus Gilbert) and his men, who suspect him to be an agent for Duke Henry, with whom Arthur is at war. He is enslaved along with the captured Duke Henry The Red (Richard Grove), his gun and chainsaw confiscated, and is taken to a castle. Ash is thrown in a pit where he regains his chainsaw from Arthur's Wise Man (Ian Abercrombie) in mid-air, decapitates a female Deadite and lops the hand off another, before escaping the pit. He decks Arthur using the "your shoelace is untied" gag. Ash demands that Henry and his men be set free (since Henry was sympathetic to him) and they ride off. He uses the shotgun to blow the end off of Arthur's sword, and to blow a large Deadite back into the pit. Ash is celebrated as a hero, and also grows attracted to Sheila (Embeth Davidtz), the sister of one of Arthur's fallen knights.According to the Wise Man, the only way Ash can return to his time is to retrieve the Necronomicon. After bidding goodbye to Sheila, Ash starts his search for the Necronomicon. Entering a haunted forest, an unseen force pursues Ash through the woods. Fleeing, Ash ducks into a windmill where he crashes into a mirror. The small reflections of Ash climb out from the shattered mirror and torment him. One of the reflections dives down Ash's throat and uses his body to become a life-sized copy of Ash, after which Ash kills him and buries him.When he arrives at the Necronomicon's location, he finds three books instead of one. Ash eventually finds the real one and attempts to say the magic phrase that will allow him to remove the book safely "Klaatu barada nikto". (The line was taken from the 1951 film The Day the Earth Stood Still). However, forgetting the last word, he tries to trick the book by mumbling the missing word. He then grabs the book from the cradle, and rushes back to the castle, while the dead rise from graves all around. During Ash's panicked ride back, Ash's evil copy rises from his grave and unites the Deadites into the Army of Darkness.Despite causing the predicament faced by the Medieval soldiers, Ash initially demands to be returned to his own time. However, Sheila is captured by a Flying Deadite (Nadine Grycan), and then transformed into a Deadite. Ash becomes determined to lead the humans against the skeletal Deadite army. Reluctantly, the people agree to join Ash. Using scientific knowledge from textbooks in the trunk of his 1973 Oldsmobile Delta 88, and enlisting the help of Duke Henry, Ash successfully leads the Medieval soldiers to defeat his Deadite clone, Evil Ash, and his Deadite Army, and save Sheila. After this, he is brought back to his own time using a potion made from the Necronomicon.The final scene (See Different versions) begins with Ash back at the S-Mart store, telling a male co-worker (Ted Raimi) all about his adventure back in time, and how he could have been king. After this, a Deadite starts wreaking havoc on the store (it is implied that he again raised the dead by saying the wrong words needed to travel through time), and Ash slays the creature. The film ends with Ash in voice over saying, "Sure, I could have stayed in the past. Could have even been king. But in my own way, I am king." He then says out loud, while kissing the attractive female co-worker whose life he has just saved, "Hail to the King, baby!"

Question: How is Sheila related to Arthur's fallen knight?
Answer: Sister