(Forays are going to be shorter pieces about music that is different from the styles that I am most familiar with. Rather than attempt in-depth reviews of musical idioms and artists I know little about, I will offer brief impressions that might interest you as well.)
The Guardian calls her the best singer you never heard. Nick Cave calls her his favourite female blues singer, and used her rendition of the traditional song 'Katie Cruel' as the basis for his song 'When I First Came To Town'.
Dalton's voice was often likened to Billie Holliday's. It has the same direct, raw feel to it. She sang in a high-pitched tone, which sounds as if it was produced mainly in the mouth with the throat clenched a little. Her voice sometimes sounds like a trumpet, and her phrasing is brilliant, sometimes more immaculate than her actual pitching. It can take some getting used to, but find and listen to her rendition of 'It Hurts Me Too' for a good introduction to her style.
She played a mean 12-string guitar, too.
She came by folk-singerdom in the old-fashioned way, never wrote original material, was reluctant to record and rarely did, and died homeless in New York city in the 1990s. But her music is not just an oddity left behind by an enigmatic, romantic character - it's very real and vastly soulful.
Go here for a discography and more links.