You can start pulling vocal or stylistic comparisons out of a hat for Nadler if you have to. There is an ethereal quality that calls to mind Hope Sandoval. Likewise there is the oddball other-worldliness that might make some think, "Kate Bush" (but certainly not ALL of the eras of Bush's career). Even one of the early, pre-dress-up-like- pirates, Heart albums spring to mind (Dog And Butterfly). One thing you won't think, you won't entertain, is that Nadler is a run of the mill folksinger.
Her voice is vulnerable and strong in the same instance and it is what soars in the music. The word "otherworldly" comes to mind again but this is not True Blood-annoying-fairy-otherworldly.