Liam McChubs mentioned Marilyn while talking to the police, so the team decided to interrogate her about Linda McChubs' murder. She said that they were good friends and that Linda was a nice person. She was interrogated for a second time and she said that she wouldn't be surprised if Liam turned out to be his sister's killer. In the end, Marilyn was proven innocent as Zack Clewn turned out to be the actual culrpit.
Marilyn became a part of Cecilia DiGiappo's murder investigation after the police found her drug baggies at the crime scene. She claimed to be just an accquaintance of Cecilia, and they used to take drugs together. She wasn't a main suspect and in fact she was innocent, being Steve Zasts the real killer.
After Zasts' sentence, she asked for help because the police had destroyed her peyote plant at the farm. Evan Day questioned her because peyote can be used as a drug, but she said that she needed it for medical reasons.