Kappel was active in many major opera houses during her career. She sang in Munich and Vienna, and 1924–1925, at the Metropolitan Opera from 1927 until 1936. She also toured as a concert singer, and made recordings. Kappel was known for her interpretations of the works of Richard Wagner and Richard Strauss, especially
Isolde,
Brunnhilde, and
Kundry. In London, she gave "a fine Brunnhilde" in 1924, Her performances as
Elektra,
Sieglinde, and
Senta in London in 1925 were described as having "dramatic force" and "uncanny eloquence". In 1932 she starred in the first production of
Elektra at the Metropolitan Opera. The following month, she was again heard on radio, in a national broadcast of
Die Walkure with
Paul Althouse and
Frida Leider. == Personal life ==