When I was about 10 or 11 (which would have been in the mid-60s), I had a piano teacher who must have been at least 65 at the time who claimed that she had traveled with and played in the shows put on by Hildegarde, who was a renowned concert pianist and singer back in the 20s and 30s.
There was another one-name pianist lady from the 1930s, billed as “Ramona.” I think Paul Whiteman hired her for a while, as an added-attraction for theater appearances. She made a few records. Light, cabaret stuff.
Could it be Hildegard Knef? (1925-2002)
“From Here On It Got Rough”
http://www.youtube.com/watch?v=4-7e4aRDtik
Hildegarde (who died a few years ago) was the original one-name celeb. Well, except maybe for: