Doctor Rebecca Hendrix used to be a cop. She and Olivia went to the Academy together and then 2 years later, Rebecca decided that her time was spent better shrinking heads and was sick of locking criminals up She would rather treat the criminals and help the victims. Elliot, who was known to dislike shrinks, surprisingly agreed to let Rebecca to facilitate in on the questioning with Miranda Cole (a rape victim with mental problems) much to Olivia's surprise. Olivia was surprised again when Elliot suggested that Rebecca to sit in during the interrogation with suspect Thomas Mathers. Olivia told Elliot that she got that he was on a rebound (he was separated at the time) but wanted him to keep it out of work- it'd be great.
Rebecca called SVU when Holly Parcel was admitted after a car accident and it was discovered that she had been sexually abused. Elliot quickly volunteered to questioned Holly while Rebecca oversaw the rape kit during questioning.
On another case involved twins, Rebecca was reported to the Medical Board for telling Lindsay Stanton the truth that she was born a boy after an accident happened ('her' penis was cut off by accident during circumcision; the parents decided to raise him as a her. After discovering the truth, Lindsay decided to become a boy again.). She had no right to. Elliot told her to take care as she was packing up her office.
A year later, Elliot turned to Rebecca for help to find out what was wrong with him after he had a fight with a former partner in court. Elliot opened up about his separation from Kathy and troubled relationship with his father.
A year later, Don arranged Elliot and Olivia to undergo an independent psychological assessment by Rebecca so he can decide if it's appropriate for them to continue working together. Her opinion was that Elliot and Olivia had a degree of mutual reliance and emotional dependence that compromised their effectiveness as police officers. They're too close. Don would lose his two best detectives if he split them up.