Fever by VK Powell 

2010, paperback 

Hired gun Zak Chambers expects to provide a simple escort service to a philanthropist Sara Ambrosini, but nothing is as simple as it seems, especially love. 

Zak Chambers is a disillusioned hired gun who longs for a connection with her life beyond her sat-phone and assignments she can't share with anyone. Her boss lines up a cushy escort job to Africa to give her time to refocus.

But the country she loved as a child holds memories she isn't ready to face. Adding to her ambivalence about returning is the immensely attractive Sara Ambrosini, head of Ambrosini Philanthropic, who sees everything through the rose-coloured glasses of wealth and priviledge. Zak's task is to provide security for Sara until they reach the future site of her primary school for tribal children in the bush country. But Zak soon discovers that Sara's stubbornness and independence aren't the only obstacles to the success of her assignment.