Marie Maurer can be heard on a number of Mapleson Cylinders
(These are zip files – left click the link, download the files, then unzip when downloaded)
As the LP notes, this is not high-fidelity sound. This is IRCC LP7006, issued in 1955, containing transfers of a number of Mapleson Cylinders, recorded live from the stage of the Metropolitan Opera House from 1901 to 1903.
Maurer appears on the following tracks:
7. Wagner – Die Walküre – Herrlichste Maid! (Act 3)
Lillian Nordica, soprano; Johanna Gadski, soprano; David Bispham, baritone; Marguerite Marilly, soprano; Camille Seygard, soprano; Marie van Cauteren, soprano; Mathilde Bauermeister, contralto; Carrie Bridewell, contralto; Louise Homer, contralto; Marie Maurer, contralto; Ernestine Schumann-Heink, contralto. Alfred Hertz, conductor