Killian orders her to retrieve documents that detail the death of an individual exposed to Extremis. Brandt arrives at the bar and discovers that Tony had already gotten the files, then passed by Homeland Security to "arrest" Tony, was only stopped by the Sheriff but she proceeds to kill him and his deputy. Brandt and Savin chase Tony to recover the files but fail in their attempt. She dies in an explosion caused by Tony in a restaurant.
Trivia
In the comics, she is the ex-wife of Dr. Theodore Sallis, the Man-Thing.
The writers envisioned Brandt as Killian's main henchman, which would return throughout the movie to fight Tony, but eventually that role was reassigned to Eric Savin.