After their top 5, I take issue both with their ranking of some people and even the inclusion or exclusion of others.

I'm not real familiar with the work of some of these women.  That is, I am not aware that
Connie Smith
Lee Ann Womack
Martina McBride
Lynne Anderson
K. T. Oslin
Roseanne Cash
Cindy Walker
are of outstanding talent (voice, instrumental skill, songwriting) or impact on the world of country music (e.g., having a large number of real hits or influencing the direction of country music), when compared to other country performers such as
Jody Miller (who wrote and performed several country classics)
Kathy Mattea (singer- instrumentalist - songwriter)
Jeannie C. Riley
Donna Fargo
Holly Dunn (very good singer who also wrote "Daddy's Hands")
The Forrester Sisters
Sweethearts Of The Rodeo (Janice Gill and the other one)

If you're going to count K. D. Lang, Anne Murray and Linda Ronstadt as "country," why not Olivia Newton-John (who had a "country" phase in her career, complete with some big hits), Joan Baez (she's performed and recorded many bluegrass and c/w songs), Nanci Griffith (who has written and performed some big hit country songs and other songs that are in the c/w genre), and Iris Dement?  Murray, Lang, and Ronstadt are singers whose work encompasses a variety of styles (pop, jazz, rock and roll, show tunes, etc.)
 
The only ones on this list that I feel definitely belong in a C/W top 40 all-time women artists list are:
 
Patsy Cline
Tammy Wynette
Loretta Lynn
Dolly Parton
Emmylou Harris
Reba McEntire
Maybelle Carter
Barbara Mandrell
The Judds
Minnie Pearl
Kitty Wells
and
Dale Evans
 

After that, it becomes pretty arbitrary -- one person was at the top of the charts for a few years in the 60s, another artist in the 70s, another in the 90s, etc.