Zak S wrote a good article about gender representations in Warhammer (and fantasy in general). Short version - it's not a problem that Slaanesh's female followers are all seminude pink punk succubi, it is a problem that Khorne, Nurgle and Tzeentch haven't employed women. So here's some more Chaos.
The fates. A coven of sorceresses. A mother, a maiden, a crone. A single eye shared between them that sees the strands of fate. Iron shears that sever the ties of destiny. Iron needles to pin prophecies into souls. A loom of air, vast as a castle, across which they crawl spiderlike and work, twist, weave. One knows, one cuts, one binds.
The twisting one. Appears as a little old woman carrying some great load on her back. A peddlar or a refugee. Always on a road between cities. She is like a snail - she is part of the pack, curls up inside it. She keeps the memories and secrets of the people she has devoured in it and treasures them all. She can be traded with but she is impatient.
The Canny women. Knowledge is male or female. The Canny women preserve all that is of woman and not of man. For this they are persecuted. Those who fear for their lives Tzeentch will not listen to. But those who fear for their secret cunning, for the death of women's lore, these Tzeentch will answer even to the witch hunter's pyre. Carried aloft on a column of smoke and goose feathers. Turned to hunt out secrets and unmake the works of men.
Typhoid Mary. Rot all through her but on the outside fine, healthy. A smooth appleskin over puffed, waspblown flesh. Nurgle spared her death and gave her the gift of skintaking - she dresses in the finest. Carries a flenser's blade. Spreads the blight where she walks. Quiet as cholera, persistent as consumption. She has lived many lifetimes.
Plague mothers. What would a mother not risk to save her child? Nurgle speaks, warm as rot, close as the rattle on your lungs. 'Little one, she need not die, though I love her so dearly. Little angel of mine, she may stay with you yet, if you do this little thing I ask.' The plague mothers accept Nurgle to their heart. Milk of pus flows from their breasts. Poison brews in their wombs. They birth contagion. Their infants sick, but not fading. Strong with sickness. They will be his tallymen.
Bile Queens. Whore and Madonna alike curse man's name when they are impregnated with poison, cursed to rot for mankind's incontinence. Some, brimful of rage do not accept their fate. Come to an old wise one who knows they cannot have their health but they can have their vengeance. A rite, an offering, they open up - a portal of flesh - they channel bile, sputum, sickness, wet decay. A vengeance upon mankind.
Cult of the Bacchae. Men rule the world, and women must carve a piece of it or fall into madness. The Bacchae carve it of men's flesh. They meet in secret, share knowledge forbidden of blades and democracy and contraception. Wear false beards and trousers. On the chosen night they claim the city as their own. Any man then is game, their flesh to claim and carve and consume.
Mirror harridans. Go into battle naked except for a disc of polished brass over their heart, their skins daubed in blood signs of Khorne's favour. When they are cut to bleed the wound opens also on their foe's flesh. To fight them openly is suicide. Poison, strangling, drowning, starvation. Or wash them clean of blood before you lay a finger on them. Otherwise best first to dig your grave and fight standing in it.
Valkyries. Chosen of Khorne. Their steeds' hooves of thunderous fire and brass trampling the clouds, sulphur trails in the air. Wield axes, wear armour of runecarved brass. Headtakers and skull splitters. They return once the battle is won and claim the skulls of the worthy fallen to add to their master's throne.