Audrey Hepburn is beyond a gamine style icon; she is a style icon. These words are thrown around pretty loosely these days with any ingenue with a great stylist and a hit outfit becoming an instant style icon. Audrey is the real deal. There are some specific things about her enduring style that make it gamine.
First, the cuts of her clothing. Audrey always wore impeccably tailored pieces. I suppose it did not hurt that she was good friends with Hubert de Givenchy, famed fashion designer. Second, her penchant for timeless, polished yet feminine pieces. Audrey could rock a trench (essential for a gamine), cropped black trousers (thinking of Funny Face), and the all important LBD. While I like her in the full glamour looks made famous in her films, when she won the Roman Holiday Oscar - I can relate to her quotidian looks and see how they work in modern times. Third, her tasteful, natural makeup. She was one of the originators of the strong brow.
I reference Audrey in movies like Roman Holiday (a personal favorite) regularly. You can look at images of Audrey from over 50 years ago that a current gamine could throw on and still look pretty and put together and not at all dated. Audrey Hepburn: forever cool, forever gamine.