The opposite of Femme Fatale. Ingenue is a female character that is beautiful, sweet, gentle, virginal, pure, morally pure, refined, (usually) naive and (very) friendly. But they are in some type of danger, like physical or even emotional danger. They are also sometimes quite a bit mischevious, and may cause trouble. Ingenues also may appear to be (or have the traits of) the good Femme Fatale.
What differs this from damsel in distress is that damsel in distresses are just heroines in danger, but ingenues also has some personalities.
Ingenues, stereotypically, tend to be German, Dutch, Scandinavian, or sometimes even British, Irish, Scottish, or French.