Shadow Undercover by Rebecca Deel

On a desperate search for her missing sister, Bridget Monihan is shot at and nearly blown up. With a target on her back and time running out, she appeals to a sniper and his black ops team for help. When someone driven by obsession counters their every move, Bridget plunges into an unfamiliar world in a last-ditch effort to save her sister.
After a mission goes wrong, Fortress Security operative Trace Young stumbles across an injured woman in a Chilean alley. Following a harrowing flight to safety, he discovers Bridget’s quest and his new assignment intersect. To save innocent lives, Trace and Bridget must take the fight into the heart of enemy territory. If the operation fails, Trace will lose everything, including the woman he loves.