Jessica 'Jess' Saunders is an agent with the TNTF.
That is a bit deceptive in that when we first meet her, she is not an operative in any way. In fact, she has only a vague idea that the Terrorist Network Task Force existed, what it actually did was a mystery. That was solved for her when operative Blake Conners explained on their first meeting that the TNTF was "relatively new" and that it "consists of members from all the various federal law enforcement agencies such as Homeland Security, FBI, NSA, CIA, NORAD, and the INS. There are representatives from the different branches of the military, the Coast Guard, National Guard, and from any agency that would be involved in the event of a terrorist attack."
As stated, she is not a trained operative at the beginning and she definitely has no interest in becoming one. When we meet her, she is a divorced woman with a daughter away at college. She is described as someone working long hours at an ad agency - "mainly to avoid the emptiness of the house". In the opening pages of the first adventure, she is realizing she really needs a vacation and it is that decision that will take her to convenience store (well, the desire for coffee took her there but while in the place, she decided to pick up a travel magazine for ideas). And that will put her in position to overhear a conversation which will prompt her to make a phone call to authorities and that will change her life forever.
Saunders - her name will change as her relationship status changes - is an attractive woman around 40 years old with light green eyes which turn to "deep, emerald green when she became angry". She might not be an agent when we meet her but she is a very intelligent and tenacious (she would say stubborn) person who has no hesitation to do what she knew to be right.