Eileen Reed is a sheriff's deputy
She is a highly motivated and resourceful member of the Colorado Springs sheriff's department, a specialist in homicide. She is also a woman who finds close relationships difficult stemming from a very traumatic early childhood. Her partner is a much younger officer names Rosen who has totally different views but considerable respect for Reed.
Making this a more reasonable fit in the spy category is the presence of CIA analyst Lucy Giometti who is vital to the series as one who can bring otherwise unknowable information to the wily Reed. Very pregnant in the first book, she nevertheless manages to help save the country.
The series never leaves the country, indeed, the farthest it strays is near-by Wyoming, but the international aspects are still present and still play a major role in the series.
Reed, as an untrained espionage agent who is forced to tackle such matters while trying to solve a murder, might seem to others like a fish out of water and she is certainly treated as such by many around her, especially the military brass. She is hardly that, though, as she is an experience homicide detective, the best that the sheriff's office has, and she approaches the cases solidly and methodically. She does not allow herself to get too excited about the comments around her as she knows what she is there for and she does it.
And she has a gun herself and can use it if pushed. And as the first book progresses and the other two books reveal, she has Giometti to watch her back. Pregnant or post-natal, a smart person does not mess with Giometti.