Knight Captain Durga is the Citadel's quartermaster, a position that she is not exactly pleased to occupy. She'd rather be out in the field using weapons, rather than in the base polishing and cataloging them.
Unlike most other denizens of the Citadel, she refrains from "archaic" language (the style of speech employed by Brotherhood of Steel members; such as Star Paladin Cross) in favor of more "modern" type speech ("yeah", "whatever", etc.).
In the G.E.C.K. editor, Durga is listed as a Knight Sergeant, however both the Official Guide and the game refer to her as a Knight Captain.
A good strategy in dealing with her is to grab any junk items lying around the Citadel (no Karma penalty) and sell them to her.
Unlike other members of the Brotherhood of Steel, Durga can be killed without repercussions from other members, as they never seem to find out. This is presumably because, in the storeroom, you are hidden from other members.