If this thread is intended only for the UK, I haven't a clue, and ignore my following comment.

I can not think of any well known and currently performing female USA folk singer with a "breathy, girly voice." Among regionally (East Coast) or locally (Piedmont area of North Carolina) female folk singers, and those that I know who sing "just for fun", I can't think of any who would match that description. I also don't think any one type, style, etc. has come to dominate what we in the USA would consider to be "the folk genre" - as broad and eclectic as that "genre" is.

Witness the nomination of the Utah Phillips tribute album, "Singing Through the Hardtimes", for a Grammy as best traditional folk album of the year.    That was certainly the closest category in which to consider it, but while many of us on Mudcat would call it folk, most of us would not call it "traditional." But Charlie Poole (The Charlie Poole Project won the nomination) would also not meet most of our definitions of traditional, since we tend to think of trad. as being ballads whose roots can be traced to ballads in the UK.