Growing up in the ruins of Washington D.C. without parents, Reilly encountered a military man who took her in and taught her everything there was to know about combat, tactics and survival. When he died 12 years later, she carried his body all the way to Arlington Cemetery, and gave him the best military burial she could. In 2273, at age 26, she founded Reilly's Rangers and began a massive mapping exercise of the Capital Wasteland. Currently, she has suffered severe wounds and is in a coma in the ghoul stronghold of Underworld.
Before she meets the Lone Wanderer, her team was held up near Vernon Square by a large pack of super mutants where she was injured and nearly killed when she attempted to escape. Reilly keeps notes of her teammates in her terminal which are written as reports. According to her computer files, she and Butcher are in a complicated relationship. In her terminal log about Donovan, she mentions having a contact in the Brotherhood of Steel.
If you constantly pick the meanest (bottom) speech option when first talking to her, Reilly gets mad and will never talk to you again.
Depending on how you wake her up, Reilly's legs are crippled and can be seen limping if you use your medical skill to wake her up. But she will look like normal if you pass Doctor Barrows' speech check to wake her up.
If asked why there are so many mutants in the area she tells you that Brick thinks that there is something in the area they're looking for, which is human abducts to dip into the F.E.V. which they need to make more of themselves with.
If you have the Gun Nut perk you get a speech option to say that you've heard of Reilly Rangers before, and that they pack serious firepower. This has no other effect but variance.
There are a few inconsistencies between Reilly's dialogue and her notes. If you ask about Talon Company, Reilly will tell about an encounter with them in which Brick, the team's Heavy Weapons specialist, almost fought with a detachment of them; where as in her report on Brick, Reilly states that Brick did indeed fire on (and nearly massacre) them. It is probable that these were separate encounters with the Talon Company, hence the differing outcomes. She also states that Theo, the ranger lost in the Statesman Hotel, was a full ranger, whereas his contract is marked in her notes as "probationary". It is possible however, that Theo was promoted after, or immediately before, his death and Reilly didn't yet write it in her log.
Do not anger Reilly at all on the occasion where you get the quest. If the Lone Wanderer does, then go and start the quest another way, she and her rangers will become hostile. However, the Underworld residents will not become hostile to the him/her and will attack Reilly.
Sometimes Reilly, when in Underworld's hospital, gets stuck in a dialogue with no exit options. This seems to occur when you listen to her quest suggestion Reilly's Rangers, choose to think about it and return later, but the quest already appears on your Pip-Boy and states "Find Reilly in Underworld". Carrying out a quick save before talking to her is recommended. [platforms tag needed]
If you have the Gauss rifle, and you remain hidden, in Underworld's hospital, then shoot Reilly while she is still unconscious, she will fall off the bed and stand up, but you wont be able to talk to her, though you are able to revive her with the required 60 Medicine. [platforms tag needed]