In her terminal log about Donovan, she mentions having a contact in the Brotherhood of Steel.
According to her computer files, she and Butcher are in a complicated relationship, which she worries may jeopardize their professional relationship. This also works the other way around, if the player character attacks Underworld residents, Reilly will help them in battle. If one attacks the rangers, Underworld residents will not become hostile to the Lone Wanderer and will attack Reilly. As later discovered, they are searching for human abductees to expose to the F.E.V., which they use to make more super mutants.
