How women, both American and internationally, have affected jazz.

I agree with the OP that with the exception of singers, women have been underrepresented in jazz.  Perhaps that is starting to change.  Here are a few from the past to highlight:

Mary Lou Williams - Brilliant writer, arranger, and pianist for Andy Kirks’s hard swinging band.  After the big band era she adapted easily to modern jazz styles and was an influence on Thelonious Monk and Bud Powell who as young musicians used to hang out at her apartment in NYC.

Mary Osborne - Great guitarist who learned directly from Charlie Christian himself!  Participated in early be-bop sessions.  She didn’t record much but her few tracks are worth seeking out.  On YouTube you can see her accompany Billie Holiday.

Lil Hardin Armstrong - Going way back in jazz history, Lil wrote several of Satchmo’s most popular early songs and played piano as well on recordings.

Back to singers, I’m also a big fan of Cassandra Wilson.

Anita O’Day is not as well known today but I think that she’s one of the great jazz singers.  Her 50’s Verve recordings are wonderful.  Watch her perform Sweet Georgia Brown and Tea for Two from “Jazz on a Summer’s Day” and be amazed.

Melody Gardot who overcame a severe traumatic brain injury

@audio-b-dog 

I would like to throw out an American singer as my first offereing. I am smart enough not to make it Patricia Barber or Diana Krall, both of whomn are excellent jazz pianists, because I’ve already seen how most "serious" jazz afficianados dismiss them right off the bat.

For some reason, Barber and Krall loom very large in audiophile circles. They remain "trendy" while a host of other female Jazz artists are ignored. I’ve tried drumming up interest in other female Jazz singers here to little avail. 

Speaking of other female Jazz pianists, Geri Allen and JoAnne Brackeen are on an entirely different level.  

Yes, indeed, Cassandra Wilson,is fantastic, I have many of her cds .I lucked out at a church thrift and got 8 of them for like a buck each.

Diana Krall

For me, she doesn’t play the piano enough anymore.

Many years ago I was listening to WBGO Jazz station, and ’who the heck is that pianist?’ (no vocals). Awesome. Turned out to be Diana Krall, so I thought of her as a pianist 1st, vocalist came later, then progressively too much vocal IMO.

I’ve seen her live, small club, medium, New Orleans Jazz Festival, Radio City with Tony Bennet.

But, lucky me, I’m in a very cool antique store in NO, when I see these legs, holy, oh my, I hope the wife doesn’t catch me staring. I hear her speak to someone, without looking up, I knew exactly whose legs they were.

It was Harry Connick Jr. that she was talking to, and lucky lucky me, Harry’s wife (former Victoria’s Secret model) comes into sight, now I don’t care if I get caught staring.