At home, Noah is having nightmares about Sheila (or is it Olivia whose having the nightmare? Hard to tell.) Noah asks Olivia to sleep in her bed. She says no but relents. He asks if Grandma Sheila is okay. He wants to see her.
At a school for special needs kids, a boy named Cody keeps getting outshouted when he tries to answer questions. Later, Cody and a girl named Mariel are working together at a table. Mariel says the new medicine her mom gave her this morning is making her sleepy.
A teacher finds Mariel and Cody in a supply closet. Cody is on top of Mariel.
SVU is called in. The teacher explains that Cody is 19 and has Autism and Mariel is 15 and has muscular dystrophy and a host of other problems. Cody says he knows that when you have sex it means you love the person. Mariel (who looks weirdly like Rollins) tells Rollins that she knows that it is rape when a boy puts what he has inside a girl. However, her mother takes over the interview and says Mariel has a lot of problems and needs to go home. Rollins is shocked by how many illnesses Mariel has had.
Benson is playing with Noah when she gets a call from Rollins that she's downstairs. She sends Noah to put his PJs on while they talk. Rollins tells Benson that she finds the mother's behavior suspicious and that she had Warner do a tox screen.
Sure enough, it turns out the girl is on medications that interact poorly with each other. Rollins and Carisi visit the mother at home and she says it must be a mistake and that she did research online to find out what supplements to give her daughter. Mariel comes out and asks to go to school but her mom tells her she's staying home and sends her away.
Rollins and Carisi interview Mariel's pediatrician who says she advised the mom against these drugs a year ago.
The detectives talk to Mariel's father (who has not seen Mariel since she was six). He says the mom won't let him see Mariel and gives them some medical records.
In the squad room, the mom is freaking out about not being with her daughter. Benson accuses her of abusing Mariel but slips up and it's clear she is talking about Sheila and Noah. The mom runs out and is held back. Mariel sees and tries to get out of her wheelchair but has a seizure.
At Bellevue, Olivet (welcome back!) interviews the mom and learns that as a child she faked being injured so that her mom would keep her home and protect her from her abusive stepdad. She tells SVU that the mom has Munchausen's by proxy and is unaware of why she is making her daughter ill.
Mariel is starting to get better but is shocked that her mom was making her sick on purpose. Rollins tells her that her mom loves her but something is wrong in her brain that makes her hurt her. When her mom shows up and tries to take out Mariel's IV Mariel tells her to leave her alone and the cops arrest her mom.
Carisi tries to convince Rollins to go home and spend time with her daughter, but she gets a call from Mariel.They arrive at her home to find her mom dead. Mariel says she killed her.
Mariel confesses to hitting her mom with a hammer to make her leave her alone. Her dad says she has been brutalized but Barba cannot look the other way and charges her with murder.
At trial, the defense calls Olivet and Mariel to make the case that the mom would never stop abusing Mariel and he had no choice but to kill her. Rollins tells Barba that Mariel is obsessed with the Little Mermaid and considered Cody her Prince Eric. That gives Barba an idea. On cross he asks about the Little Mermaid and the judge gives him a short leash to prove relevance. Mariel screams that she is a real girl, not a mermaid, and her mom blocked her from seeing Cody. She's glad she's dead. She's glad she killed her.
Barba tells Benson he feels terrible about this case. The girl is 15 and has been abused her whole life and he is sending her to prison. He cannot drop the case because he feels that sends the message that it's okay to do whatever you want if you are a sympathetic defendant. He doesn't know what to do.
The next day, in the elevator, two jurors overhear Barba talking about the case on his phone. Barba tells the judge. She declares a mistrial. Barba asks for the new case to be sent to family court. The judge warns him he'd better not have ruined the case on purpose.
Benson sees Barba and tells him she has faith in him. Barba reports to her that Mariel got 3 years probation and community service. Benson considers that justice.
Rollins goes home. After feeding Jessie, she calls her estranged mom to say hello and let Jessie say hi to her.