Windmills of the Gods by Sidney Sheldom

"Windmills of the Gods" is the story of a woman trapped by a diabolical international conspiracy. The action races from the President's Oval Office to the hot Latino beat of Buenos Aires to the romance of Paris and Rome to the shadowy dangers of Bucharest.
Caught in the web of this chilling tale is Mary Ashley, a bright young professor of Eastern European studies at Kansas State University and mother of two, who is appointed the United States ambassador to an Iron Curtain country. Even before she takes up her post she is marked for destruction by unseen and powerful enemies, including Angel, an accomplished assassin who has never failed to carry out a murder contract.

Alone and a stranger in a foreign country, Mary Ashley finds herself involved with two dynamic men: Mike Slade, a tough career diplomat who is her deputy chief of mission; and Louis Desforges, a doctor attached to the French embassy. But soon she comes to believe that one of them is out to kill her.