Magda Plasky (Danielle Skraastad) is the villainess of "Child's Welfare", episode 13.16 of Law & Order: SVU (airdate February 29, 2012).
Magda was originally a nurse at Newark General at New Jersey and the wife of John Plasky, and as revealed over the course of the episode, the couple were serial kidnappers. Their first known victim was homeless teen Laurie, with the couple offering her a ride before drugging her and holding her captive in their basement, where John would repeatedly rape Laurie.
During her captivity with the Plaskys, Laurie tried to scream for help when she heard the police arrive (revealed to be from when Magda's nephew was accidentally shot), but Magda gagged and drugged Laurie before anyone could hear her. Eventually, Laurie was impregnated by John and gave birth to a baby boy, which Madga placed outside of her hospital when John refused to keep the baby (due to the child being a boy). Soon after, Laurie was released by John and Magda and the villainous couple moved to New York, with John becoming the superintendent of their new apartment building and Magda getting a job at Mercy Hospital as a neonatal nurse.
Prior to the episode's events, John and Magda abducted 13-year-old Celia Barber, pulling her into their van as she was biking with her father. As a result of John's rape, Celia became pregnant, which she was allowed to keep due to the baby being a girl. But later on, Celia gave birth to a male child, which Magda left outside a church near Mercy Hospital. The infant was found by two homeless people, and the SVU squad picked up the case.
Magda's reveal as a villainous conspirator and kidnapper came when the detectives uncovered the 4th of July incident, with the head nurse revealing Magda's previous employment in New Jersey. Realizing her guilt, detectives Nick Amaro and Amanda Rollins confronted Magda, who eventually confessed to working with her husband in his depraved actions and stated that she made sure none of the babies their victims had were harmed.
Believing Magda to be an innocent woman pulled into her husband's crimes, the detectives asked her to show them where Celia was, with Magda taking them back to the dungeon where she and John were keeping Celia and her daughter. Amaro instructed Magda to call John and lure him to the dungeon, but instead, the evil Magda warned John (in a foreign language) that the police were there, allowing him to flee. Amaro was ultimately able to capture and arrest John, and he was arrested along with Magda (offscreen).