From my friends at hollywoodmemoir.com
Agathe Johanna Erwina Gobertina von Trapp (March 12, 1913 – December 28, 2010) was the eldest daughter of Baron Georg von Trapp and Agathe Whitehead. She was a member of the Trapp Family Singers, whose lives were the inspiration for the play and movie The Sound of Music. She was portrayed as the character "Liesl".
http://www.hollywoodmemoir.com/agathe-von-trapp