Very little is known about the woman addressed as Miss Knox and even less about her can be verified. In practice she is the first female Secret Service agent in history, but any additional information on her leads to the office of Secret Service Chief Wilkie - where it stays hidden.
Not without Precedent
Although unconventional, it would not have been completely uNPRECEDENTED for a man like Chief Wilkie to hire a woman like Miss Knox for presidential security.
The Killer Angel
No matter who Miss Knox is or where she comes from, one element to her biography appears to be genuine. She is indeed a former student of Edith Margaret Garrud's school of jujutsu in London, and likely one of the few students Mrs. Garrud trained in ADVANCED jujutsu techniques. Such classes were open only to members of the British women's Suffrage movement as a safeguard against policemen who tried to arrest them.