The treatment Olivia is doing in the beginning is EMDR therapy (eye-movement desensitization and reprocessing therapy) is a method proven to help people recover from trauma and other distressing experiences in life. It is usually used with talk therapy with a licensed therapist or counselor.
Amy Carlson (Katie McGrath) plays her first role in the Law & Order franchise since her main role as ADA Kelly Gaffney in the short-lived series Law & Order: Trial by Jury, which aired from March 2005 to January 2006.
During her EMDR session, Benson mentions the following missing persons from previous episodes; Heather Hallander from S10.E11 "Stranger", Nate Holland-Martell from S13.E05 "Missing Pieces", Hector Rodriguez from S14.E05 "Manhattan Vigil" and S17.E09 "Depravity Standard", Bailey Shaw from S20.E17 "Missing", and Emma Lawrence from S19.E05 "Complicated".