Why she was suspicious:Jenna mysteriously returns to Rosewood and meets up with Sara Harvey. She lies about the reason she's back, and we later find out she wants to know what exactly happened to Archer and Charlotte. After Sara Harvey's death, it's easy to implicate Jenna, who'd been working with her.
Why she's innocent: At the end of the episode, Mary Drake knocks Jenna out. We see a shadowy figure drag her away. When she wakes up, she's in a car with a person in a black hood in the driver's seat. Jenna then says out loud that the driver is "A.D.," meaning it couldn't possibly be her.