Crystal is the wife that Raymond Holt made up as a part of his story to distract the parking lot attendant at the prison Rosa Diaz was at in the episode, The Big House Part 2.
Holt's job was to distract the parking lot attendant while Charles and Amy broke into Melanie Hawkins' car to upload a mirroring app on her phone.
The story he used was how he was struggling to work up the courage to see Crystal, his female wife. He was cheating on her with a waitress from Wing Slutz and Crystal caught them. At the time, she was serving 5 years for aggravated assault.