 Cosima Wagner, the composer's widow, became her mentor at Bayreuth, and she proceeded to perform all the main Wagnerian soprano parts at the festival prior to the outbreak of World War I in 1914.She first sang at the Vienna Hofoper on 8 December 1897, when she took the role of Brünnhilde in Die Walküre under Hans Richter.Mahler put her on a contract and she soon experienced enormous success.