Margaret Murphy is an administrator at St. Thomas Hospital and disapproves of Tara's relationship with Jax and the Sons of Anarchy. When insurance issues meant that Chibs would be removed from St. Thomas before he made a full recovery, Gemma confronted Margaret about the situation in an elevator at the hospital. Margaret then filed an insurance fraud complaint accusing Tara of coaching Chibs to fake symptoms in order to extend his stay at the hospital and had Tara's hospital privileges suspended. When Margaret's meddling becomes too much, Tara accuses Margaret of putting the hospital profit dangerously ahead of the quality of care and threatens her to back down or SAMCRO will cause her harm. When Margaret refuses, Tara brutally beats her down.
Margaret becomes more supportive of Tara and encourages her not to waste her surgical talents. She is with Tara when Hector Salazar and his girlfriend, Luisa, take Tara hostage. When Tara claims Margaret has nothing to do with SAMCRO, Salazar lifts up Margaret's shirt to reveal a massive biker tattoo covering her back. Held captive by Salazar, Margaret reveals to Tara that when she was young, she ran with a biker gang, doing drugs with their leader, who she was in love with. On Christmas Eve, 1989, the two overdosed on heroin laced with Fentanyl, the biker dying and Margaret spending several months in a coma. When she awoke, she decided to turn her life around and kept the tattoo as a reminder of the life she left behind.
Tara mortally wounds Luisa with a piece of broken mirror and negotiates Margaret's release. After their ordeal, Margaret becomes far more caring toward Tara, insisting the woman leave Charming to get a fresh life and going so far as to confront Gemma on not wanting to let Tara leave. She also gives Tara a recommendation for a hospital in Portland.
Margaret spent season 6 helping Tara lie and manipulate Jax, Wendy, Unser, and Gemma to try divorcing Jax and taking her kids away from them and SAMCRO.