Origin
Harriet Best, A.K.A. U.S. Annie, was one of many heroes who joined the Anti-Registration Underground. She was presumably arrested by S.H.I.E.L.D. when they discovered the location of the Underground.
Creation
U.S. Annie was created by Paul Jenkins and Ramon Bachs, with her first (and only) appearance being in Civil War: Front Line #4 – Embedded, Part 4.