According to the Internet source given below, Edna Thornton was an English contralto born in Bradford.
She had a long career with the major British opera companies, particularly as an interpreter of Wagner. Thornton worked at Covent Garden and toured with the Quinlan and Beecham companies. After the British National Opera Company was established she worked with it extensively .
She died in Worthing.

Websites:
	Edna Thornton	Brief biography by operascotland.org

This list is derived from information provided by Monologues.co.uk which went down sometime in 2023.
The loss of this valuable resource is very sad and a mystery.