The only female vocalist I listen to that is for sure jrock is Cocco, this is my favorite song from her.
Cocco - Kumoji no Hate
I don't have my Love Psychedelico cd with me, but they're rockish, and they have a female vocal.
Judy and Mary is...sort of rock. o_O
Judy and Mary - Sugar Cane Train
Favorite songs from other j-rock bands (none of these are the makeup wearing femme men bands. I can't seem to find one of those who's vocalist doesn't irritate my brain. x_x).
Asian Kung-fu Generation - Loop & Loop
ELLEGARDEN - Lonesome
OCEANLANE - Ships and Stars
Hanaregumi - On Time (acousticy rock)
SPITZ - CHERRY (Words can not begin to describe my love for SPITZ and for this song. One of my favorite songs ever written.)
THE BACK HORN - Aoi Sora(there's some yelling in here, but it's not too grating on the ears)
Straightener - Rocksteady
The Pillows - Little Busters
Chikuzen Sato - Carnival (Pillows cover)
Bump of Chicken - Hybrid Rainbow (another pillows cover, the only thing I've heard from them, but it's very good)
Porno Graffitti - Ageha Chou
Others have already reccomend Shiina Ringo, but this is the only song I've heard by her that I like. It's a SPITZ cover, and it's almost better than the original.
Shiina Ringo - Supika
These three are less rock and more pop, but they're not Ayu and Momosu kind of pop. I love them, and I didn't see them on either micster or walking_proud's playlists so...
Tsuji Ayano - Clover
Tsuji Ayano - 愛の真夏 (more 'rockish', with James Iha on guitar and bg vocals)
Chara - Skirt (also with James Iha, western artists who work with japanese artists are love)
Bonnie Pink - Souldiers
And if anyone would like to hear more from any of them, I'll be happy to upload more stuff.
EDIT : Ahh. It's too early in the morning. XD I forgot to do my html in BBS type. x_x; I'll fix it. ...fixed! XD *is dumb*