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The V star will play a piano teacher suspected of killing one of her students in an episode due to air on March 30.
"[It's] so dark [but it's] terrific stuff," she told TV Line. "It definitely opened my eyes to a lot of things I didn't know about."
Mitchell added that she had also enjoyed working with Jeremy Irons, who reprises his guest role as a sex therapist in the instalment.
"I've always wanted to work with him, so that was nice," she said.
Law & Order: SVU continues on Wednesdays at 10/9c on NBC.
