Most underrated female recording artists..

Jackie Ryan/Jazz with Latin influence

Amy Helm/Americana (Levon's daughter) 

Linda Thompson/British Folk-Rock (I think her work with Richard is better than her own solo recordings) 

Courtney Marie Andrews/Contemporary Folk/Americana Singer-Songwriter

Allison Russel (with Birds of Chicago)/ Contemporary Folk with a spiritual perspective

Kris Delmhorst/Contemporary Folk Singer-Songwriter

Lindsay Lou (with the Flatbellies)/Contemporary Folk with Old-Timey influences

Rita Hosking/Contemporary Folk with a Country flavor

Dori Freeman/Contemporary Folk with Classic Country leanings, although her latest (which I don't care for, personally) is more rockish. 

Jaqui McShee with Pentangle/British Folk, Folk-Rock with Jazz influences 

Sloan Wainwright/Contemporary Folk Singer-Songwriter

Maya DiVitry (in Stray Birds)/Americana with Folk and Bluegrass influences 

Terri Garthwaite (with Joy of Cooking) 70s Bay Area band with Blues and Country influences 

Cris Williamson (Women's Music but not just for women)

@brunomarcs 

 "How about 'Female artist never heard of' I think that's what this has turned into.  Now you audiophiles have heard of many more than the average consumer probably 90% of these lady's mentioned wouldn't be recognized by the majority and some should not be on any list. It's amazing how we all have different opinions on what we like".

You presume popularity and artistic merit are one and the same.