She was born in Munich, Germany in 1977 (but grew up in Berlin), to a German father and Korean mother.

She is also a regular performer of chamber music, and has appeared at festivals including Ravinia, Marlboro, Schleswig-Holstein, and Salzburg, partnering with other musicians including Yo-Yo Ma, Pinchas Zukerman, Yuri Bashmet, Julia Fischer, and her sister, Nicole.

In May 2010 her recording of Vieuxtemps' 4th and 5th violin concerti, as well as his Fantasia Appassionata, was released by Hyperion, and features Martyn Brabbins and the Royal Flemish Philharmonic.

She won the Young Concert Artists International Auditions in 2000 and a Borletti Buitoni Trust Award in 2004.

Hagner is also a friend and supporter of the Freya von Moltke Foundation, playing in some successful benefit concerts and events.