Complex sentence: In July 1939 she became the first Frenchwoman to sing Isolde at Bayreuth (conducted by Victor de Sabata), and here she established friendships with members of the Wagner family.
Split into simpler sentences: In July 1939 she became the first Frenchwoman to sing Isolde at Bayreuth (under the baton of Victor de Sabata). At Bayreuth, she established friendships with members of the Wagner family.