Sentinel Lyons

Sentinel Sarah Lyons was a Brotherhood of Steel member and the commander of the Lyons' Pride in 2277. She also served as Elder after her father passed, but was killed in combat.

Background
Sarah Lyons was born in 2251 in the Brotherhood of Steel's Lost Hills bunker in California.

Some time after the Chosen One stopped the Enclave on the West Coast, the Brotherhood of Steel ruling council decided to send a contingent of soldiers to the East Coast with a mandate to recover all advanced technology from the Washington D.C. area and to investigate the reports of super mutant activity in the area.

And so, when she was three years old, (and her mother having died several years earlier), a small but hardened contingent of Brotherhood of Steel soldiers, led by Sarah's father, an idealistic paladin named Owyn Lyons (accompanied by his friend and technological adviser Scribe Reginald Rothchild) set out from the Lost Hills Bunker in California. This started the long trek east to what was once Washington D.C.

A permanent base known as the Citadel was built into and beneath the ruins of the Pentagon. Owyn Lyons, now Elder of the Capital Wasteland division of the Brotherhood, and his soldiers also found the super mutants in the urban ruins of downtown D.C. and helped to stop the mutant tide from overtaking the entire region.

In 2277, Elder Lyons' daughter Sarah is now a grown woman, but she is still one of the Brotherhood’s finest warriors, if not the fiercest. In fact, she’s the only member to have achieved the illustrious rank of Sentinel, and now commands her own elite squad, Lyons' Pride.

Sarah is, unsurprisingly, loyal to her father, but her superior attitude to wastelanders is more typical of those in the Brotherhood with lingering sympathies for the Outcasts. She has little patience with 'civilians' stumbling into the line of fire. However, this may be the pride of a professional rather than someone who doubts the value of the Brotherhood's objectives. Her attitude to Initiate Reddin suggests she is not convinced that wastelanders should be recruited into Brotherhood ranks.

After her father died, Sarah assumed the position as the new elder. Shortly after her nomination, she died in combat. The data is found in the Prydwen's terminal entries.

Quests

 * Following in His Footsteps: The Lone Wanderer encounters Sarah while traveling to the GNR building plaza. The PC will find her squad not far from the Tenleytown/Friendship station exit to Chevy Chase North. When the PC approaches her, Sarah will not trust the wanderer but will allow them to follow behind them to the GNR studios. Upon reaching the GNR building plaza, the PC and Lyons' squad will be attacked by super mutants and a super mutant behemoth. Lyons will then enter the GNR building with the remainder of her squad. While there she can be talked to, and will thank the PC for his or her help if appropriate.
 * The Waters of Life: Sarah accompanies her father when he receives Dr. Li, her team and the Lone Wanderer at the Citadel's courtyard. Once the Elder has finished his conversation with Li, Sarah will unsuccessfully try to convince her father to let her team attack the Enclave immediately.
 * The American Dream: Once the Lone Wanderer has escaped from (and possibly destroyed) the Enclave's base at Raven Rock, Sarah will once again attempt to convince her father to let her team try to retake the Jefferson Memorial. While Elder Lyons initially refuses, once he hears that the Enclave have acquired the G.E.C.K. and thus possess the technology to reactivate Project Purity, he agrees to greenlight the mission.
 * Take it Back!: Sarah, after inducting the Wanderer into the Pride, briefs her team on the mission to come. She personally accompanies the Wanderer into the Jefferson Memorial Rotunda for the final confrontation with Colonel Augustus Autumn and his handful of personal guards. Based on the Wanderer's choice, Sarah Lyons will:
 * Watch the Wanderer's selfless act of sacrifice in choosing to enter the chamber and mourn their inevitable demise (unless Broken Steel is installed).
 * Enter the chamber herself, sacrificing herself in place of the Wanderer.
 * Wait until the Purifier explodes.
 * Who Dares Wins : After the player escapes from the mobile base, Sarah Lyons will appear again (unless she was killed) and pick the Lone Wanderer up in a Vertibird, taking you back to the Citadel.

Effects of player's actions

 * She will comment if the player character is wearing power armor when fighting the behemoth in the GNR plaza, saying they can wear it for helping them defeat it.
 * If the Lone Wanderer activates the purifier themself, or uses Fawkes, Sergeant RL-3 or Charon to start it; it is revealed that an energy spike knocked her and the Lone Wanderer unconscious. Two weeks later after the Lone Wanderer wakes up, she's still in a coma, "unresponsive but stable".
 * If Lyons activates the purifier, she will be killed by the radiation and doesn't appear again.
 * After completing all the main quests, if the Lone Wanderer chooses to destroy the Enclave, she will comment that she wishes she could get to know the Lone Wanderer better, hinting possible feelings for them.
 * If the Lone Wanderer betrays the Brotherhood instead and launches an orbital strike on the Citadel, she and the other Brotherhood members who picked the Lone Wanderer up will attack in a fury, calling them a traitor. It is then possible to kill her, as she will no longer be essential.

Appearances
Sarah Lyons appears only in Fallout 3 and its add-on, Broken Steel. She is also mentioned in Fallout 4.

Behind the scenes
Fallout 3 Faction Profile – the Brotherhood of Steel by Emil Pagliarulo.

Bugs

 * At the end of the game Sarah Lyons can glitch into either saying that "the control room still isn't clear" or repeat the phrase "Steel be with you!"
 * After The Waters of Life, before speaking to Rothchild to start the quest Finding the Garden of Eden, Lyons will appear on the road leading from Arlington Library to the Flooded Metro, walking along the road to a point past the Nuka-Cola Plant.