Sheila was originally from the year 1300 AD, where she was a damsel in Arthur's castle. When Ash showed up in her time she slowly fell for the choosen one. It is hinted that they made love but he had to return to his own time and Shelia became bored. She was breifly pocessed by the Necronomicon but when Ash defeated it once again she was freed.
Sheila became bored again and begged the wise man to send her to Ash's time so she could help him, after much convincing he told her how she could open a time portal. She was able to and meet Ash while he was in Egypt.
Ash got Sheila a job at S-mart untill it became over run with deadites. Two of her co-workers, Buck and Iggy, work closely with Ash in order to save Sheilia and another endangered woman, Mindy. However, out of the group, only Ash and Shelia survives. The Necronomicon is seemingly destroyed after being stunned with Buck's secret stash of alcohol. Williams is later put into Arkham Asylum. Sheila kept trying to help him until she disappeared. Ash later discovered she was trapped in a Mirror Universe much like Alice's Wonderland. Sheila had established a small safe house and allied herself with two older gentlemen.
The Sheila character was orginally played by Embeth Davidtz in the Army of Darkness movie.