The actress plays a piano teacher accused of killing and sexually assaulting a young girl in tonight's episode of the crime drama.
She told TV Guide that her character June Frye is "so damaged and so violated", adding: "The episode is really, really, really dark, but there are twists to the story and it isn't all what it seems."
She added: "We don't know if [June] did it or not. I think you'll be intrigued by it, if you can stomach watching it."
Mitchell admitted that she initially had some reservations about tackling such a sensitive subject.
"I'm pretty clear about what I will and won't do, so that was taken into consideration," she explained. "As a whole, we were pretty honest and pretty respectful. I'm hoping to shed some light on a situation that we don't talk about very often."
Jeremy Irons will also appear in the episode, reprising his guest role as sex therapist Captain Jackson.
Law & Order: SVU continues tonight at 10/9c on NBC.
> Elizabeth Mitchell: 'SVU role is terrific'