Jo Ann Geary is an officer with the U.S. Air Force Special Operations.
She holds the rank of Captain when we first meet her. While it is not known how long she has been in the service, it has to have been more than a couple of years for her to bump up to O-3. And doing so while working in Special Operations means she really had to show she knew what she was doing, especially taking place in the early 80's as they do, a period not known for decent advancement for women in the military outside of clerical duty.
If she had been in civilian life, she would have fit in well with the CIA. Being military, though, it is surprising DIA has not snatched her up, though it is possible they tried. This woman is highly competent, quick thinking, very motivated, and gutsy as all out.
Geary is Caucasian from her father and Korean from her mother. Based on flashbacks we know she was born in 1950 which puts her at 31 when the first story takes place. Her early years were rough being of mixed ancestry and growing up first in Korean where her father worked in the embassy then in Japan. She had only a few friends and far too many bullies who enjoyed taunting her - at least until she had had enough and struck back.
Her mother, to help her understand why she was being picked on, told her the tale of a white fox who was very, very old and survived by being able to transform himself into any animal he needed to be for protection. Her mother told her she would be like that fox and could use that skill to "protect yourself and help others. You will be a female fox, though. A vixen". Hence her nickname.