All that can presently (June 2022) be gleaned about Mabel La Blanche from sheet music covers and by Internet searching is that she was presumably an English actress/singer who has been featured on 2 works published between 1904 and 1906.
Surfers are welcome to contribute any further information about this performer.
This list is arranged by composer and contains 2 works performed by Mabel La Blanche who is featured on sheet music covers.
It does not claim to be complete and represents only the number of items located. Keys:(w&m)