The only one I can think of is Lou Christy, a guy from around that time. I know you're looking for a woman singer, but this guy has a very high voice.
Or these guys?
http://en.wikipedia.org/wiki/The_New_Christy_Minstrels
I have a feeling I've been of no help at all.
<goes off, finds sample> Nope, definitely not him! She really did sound like Ella Fitzgerald, but less rich.
Nope, but it's fun being reminded they exist
This may be the musical mystery of the century. It's quite possible that this single was sent out to radio stations, but never released to the public.
Yeah, I'd really like to help. Kind of a challenge at this point. I'm gonna keep digging.
Was it just her voice quality that sounded like Ella? Not the genre, right? If she was a jazz singer I might be able to track her down.