Who are your three favorite female singers?

Heather Masse
Alison Krauss
Rhiannon Giddens
Margo T
Eva
Linda R
Patti Griffin
Sandy Denny
Tata
Astrud of course
......
this list is endless, as it should be

Conformity is the jailer of freedom - JFK

and because
....
Foolish consistency is the hobgoblin of little minds.. Emerson

three easy has it correct....

Janis Joplin
Norah Jones
Billie Holiday

Off the top of my head...
Janis Joplin
Elly Ameling
Ella Fitzgerald
Edited to deal with this website's damnably clumsy posting regimen.

Loreena McKennitt

Ann Wilson

I'll leave it right there.

I had the pleasure of seeing Heart live and the Wilson sisters were in their prime and just nailed the performance.  It was in an acoustically great performing arts center at a Big Ten school...quite a night.  It was some time back, as their warm up/lead in act was The Little River Band. One of the best live events I have seen. 
Perhaps my favorite live events were the three times I saw Jackson Browne.