Mary Lou Summers, also called Cheryl, was the hidden main villainess from Howling V: The Rebirth and The Howling: New Moon Rising.
She was portrayed by Elizabeth Shé.
Mary Lou Summers was one of a group of random people who all came together in a castle in Budapest that had been closed for 500 years. It was later revealed by the host, Count Isht Van Bezeli, that they were all descendants of a family that occupied the castle back then and had all committed suicide, while a baby who carried the werewolf curse survived. Because of this, one of the descendants is a werewolf who had been killing the others one by one. At the film's end, Mary Lou runs into the Count, who accuses her husband, David, of being the werewolf. With the full moon close to rising, Mary Lou points a gun at David and the Count, with the latter telling her to shoot her husband. Instead, she shoots and kills the Count and embraces David, who tells her that there are no werewolves. In the final scene, however, Mary Lou turned heel when she smiled evilly after the full moon appeared, revealing herself as the werewolf and howling as the film ends.
In The Howling: New Moon Rising, Mary Lou resurfaced in a small California town under a different name, Cheryl, and continued her murderous acts as a werewolf. She was planning to frame a tourist named Ted Smith as the werewolf, and she lured him to her home and pointed a shotgun at him; planning to kill him. Once she fires, it turns out that her gun was loaded with blanks, and Ted and a local detective had set her up. Later in the scene, the evil Mary Lou opened the curtains, stared at the full moon, and transformed into a werewolf. After her transformation, Werewolf Mary Lou bursts through her front door, only to be shot and killed by several people who were outside waiting for the werewolf to appear.