Thanks! This is exactly what I was looking for!
Hey you!, I’m going to try not to pass any of these ladies up. This is all really great stuff here.
Yup, two albums. The first was self-titled, released in 1979, the second, called “Six of the Best”, release in 1980. They were actually a South African all girl group. This page has their history.
I’m a HUGE Guess Who fan! I have most of their albums on vinyl, including “Artificial Paradise” with all the cool insert stuff. I also, of course, have it all in CD, too. I also corresponded for a while with John Einarson, author of the the Guesss Who biography book, and got a signed copy from him. If you haven’t read it, it’s really interesting. Oh, and I have all that’s available of Burton’s solo work on CD.
Yet “Bobby McGee” is the only one that gets played on the radio these days. 
4 Non Blondes
Letters to Cleo
The Distillers
Lunachicks
Luscious Jackson
Belly
Throwing Muses
Sonic Youth
PJ Harvey
Liz Phair
Veruca Salt
Ani DiFranco
K’s Choice
Heather Nova
Juliana Hatfield
Mazzy Star
Garbage
Poe
Susan Tedeschi
Just a couple for now.
I mentioned Patti Smith’s name earlier, but I would like to elaborate and recommend her. I think a fan of Janis Joplin would like her.
I guess I should have the read the whole thread before posting a bunch of nineties artists.
Oh well, since I am on a role
Drill
Tracy Bonham
Alana Davis
Joan Osborne
Dar Williams
I think I am done now.
I am chagrined that nobody has mentioned Nico. Chelsea Girls is one of my favorite albums. She had the most amazingly sad voice. Nobody sounds at all like her. But, maybe you don’t want to listen to music that makes you want to blow your brains out…
Sadly, now that I think about it, Patti Smith, Joni Mitchell (only Blue) and Sleater-Kinney are about the only other females I have in my collection. I am female. Maybe I should open a thread where people suggest things for me.
Wanda Jackson
Janis Martin
Tina Turner (I’m a big fan of her early '60’s stuff with Ike)
The Slits Betty Davis
X
The Avengers
The Rezillos
'50’s - '80’s? Yep. Classic Rock? As far as I’m concerned.
Well, they also play Piece of My Heart, but yeah, that’s about it.
Another obscure one I just remembered:
Storm
Another two-album group. Interesting because their first album was self-titled (“Storm”) and their second album was self-titled (“Storm”). And no, the second is not, in fact, entitled “Storm 2”, they’re both just “Storm”.
Hey, use this one, I don’t mind 
I was actually thinking of Piece of my Heart as the Janis Joplin song they always play, so maybe there’s actually two Janis Joplin songs.