Petra is a patient in Dr. Marcel's mental asylum and she makes her debut appearance in Edna and Harvey: The Breakout.
Petra appears as a young woman who has blonde hair done up in two braids, each of them with a red decorations. She has large eyes and is seen constantly smiling.
Petra is discovered by Edna in one of the asylum's restrooms. She jumps out, surprising Edna. Realizing she is not the one she intends to surprise, she calms down. After being asked what she is doing and why in a restroom, Petra states that she is throwing a surprise party for Peter, and in her opinion, the restroom would be the most fitting place for it. Soon after, Edna leaves with her bean dip.
She is seen later in the restroom again with Peter, and then in the cafeteria with him.
Petra is found in the role-playing room with Peter, Drogglejug and King Adrian. In the role-playing game, her character's name is Petrulla, a magician. In Hoth Motigor, Petrulla was tasked in not only ensuring that the kettle wouldn't whistle for the NPC, but also make some herbal tea for him. She starts falling asleep after Lilli as Lilligrim tells her that she would be watching the kettle. Soon after the NPC's death, she is seen with Peter (as Snippo), Droggeljug (as Sir Droggelot) and Lilli fighting against the goblins at the Valley of Uncomfortable Memories. She is last seen still playing Hoth Motigor with her friends as she asks if they get EXP from their experience.