She was played by Rebecca Tilney.
Crystal Shoemaker is a social worker and the revealed villainous mastermind behind a scam that included taking Cheyenne boys from their homes and placing them into foster care, all for profit. She colluded with fellow worker Ryan Shank in the scam, which included instilling a plant to make false allegations regarding abuse in the homes. The children are taken from the homes and sent into White families, and as a result, Crystal received a huge payout, which she shared with Ryan.
However, Ryan was beaten up by Hector, a watchdog working for Cheyenne advocate Jacob Nighthorse, and following this, he phoned Crystal and planned to come clean about their scam. Crystal had no intentions of confessing, so after she received the call, she drove up to Ryan and ran him down in her car, killing him. The villainess used Ryan's description of Hector (a tall Cheyenne with a scar on his face) to frame him for the murder, and she covered her own tracks by ramming her own car and claiming that Hector assaulted her.
After Longmire released Hector from jail, he went to Crystal's home and revealed her evil scheme to her. Crystal denied the claims at first, claiming that she'll do whatever she'll have to do for the children, but after outing her as a self-serving sociopath, the evil Crystal showed her true colors and stated--in her own words--that she'll get away with her crimes because she's a White, upstanding citizen. However, Longmire reminded the arrogant villainess that Hector knows about her scam, and that she would be better off turning herself in rather than face Hector's wrath, before leaving her home. Just as Longmire is about to get inside his vehicle, a fearful Crystal walked out the door and turned herself in to save herself.