Valaya is the third (and least important, because...reasons) of the trio of ancestor gods to the Dawi race despite being the most important to their development. The other two, Grungni and Grimnir are both her husbands (polyandry is not uncommon as Dwarf females are only 10% of the Dwarf population, and marriage is more political to tie Clans and Guilds together than anything representing love; its been suggested in the fanbase that the females find love among their husband's family rather than in the husband himself).
As a mortal in the ancient pre-Chaos era, Valaya personally founded most of the important Dwarf Holds including the Dwarf capital and later her holy city of Karaz-a-Karak and Karak Eight Peaks (although the founding is generally attributed to the kings, her sons with Grungni and Grimnir, instead). She also invented the Dwarf language including runes, although her hubby Grungni is the one that began imprinting her language into things to make magic. She also created the Dwarf culture as it is currently known, with hubby Grimnir taking over her system of control involving Grudgekeeping and Oaths. As a god she claims healing, unity, booze, home, and everything else not directly tied to Grimnir and Grungni. While she technically has a war aspect, where she trades a beer and baby for a magic axe named Kradskonti (Peacegiver) and shield, this has never been elaborated on. Her most important contribution is after Grungni predicted the collapse of the Warp Gates she created a special magic rune which repels Chaos influence as well as magic; this rune has been of extreme importance to Dwarfs ever since and provides much of their resistance to the Ruinous Powers and their strength in fighting Vampires, Chaos, Greenskins, and Elves.
Although by default females attain a high rank in society due to their scarcity and necessity for a Clan to exist, they can never achieve the highest ranks due to those being reserved for warriors (this is because Warhammer is a wargame, and one made by a company notorious for...difficulty and unwillingness in producing non-Elf female sculpts). In fact only a single post-Slotta female, Queen Helgar Longplaits from The Grudge Of Drong, ever had a model and the lore emphasizes how rare her position was. This is reflected in Valaya's lore. Despite being the goddess of home and Holds, as well as basically everything good and important other than Smithing and War, she is usually unmentioned and her people are always referred to by connection to her husbands despite her being the mother of the entire race (for perspective, imagine if Elves were referred to as the sons of Asuryan (god of magic) and Kurnous (god of war) with Isha (god of literally every other thing) almost never getting a mention despite being the only other Elf god). For a Dwarf god of alcohol in a pantheon of three to be as neglected is somewhat remarkable, to the degree that almost all information on her comes from Warhammer Fantasy Roleplay putting her on par with "relevant" gods like Ranald.
Valaya and her priests wear purple and gold robes and gowns and usually chainmail. Symbols of brewing and harvest, the home, and children represent her. She herself appears as an attractive blond Dwarf woman who's plaits reach the ground and are as impressive as the beards of her husbands.
Her relationships are fairly standard for Dwarfs. Beloved kin of other Dwarfs, refuse to admit that Chaos Dwarfs exist, close friends with humans of the Empire, neutral to other humans, dislike Elves (only barely recognize there are more than one kind of Elf and attribute the actions of evil and feral Elves to the whole race), hate Chaos in all forms, and HATE Greenskins and "RAT FURRIES GOING FULL NORTH KOREA".
In End Times Valaya was revealed to have let herself go dormant like Arianka, powering up Valaya's Gate which when opened would have brought about a new golden age for Dwarfs...somehow. Thorek Ironbrow blew himself up trying to protect her from Queen Neferata, which failed. Neferata summoned Nagash, presenting Valaya as a gift for him in order to become a Mortarch. Nagash drained the sleeping Valaya of her all magic, but left her alive.
In the final battle the entire Dwarf race gathered for one last showdown, to die fighting the Warp itself and in doing so avenge all Grudges. Grungni and Grimnir themselves appear and participate, Valaya is unmentioned but likely appeared. Whether she survived the setting is unknown.
In AoS, female Dwarfs (now called "Duardin") are entirely unmentioned and are only implied to exist by mention of marriage and fathers.
While Grimnir (now Gotrek) and Grungni survived and formed the new pantheon, no Valaya or Valaya replacement is mentioned. She HAS "appeared" because she is represented with a mighty statue in Barak Thrying, the most conservative port of the Kharadrons. So at least her legacy lives on.
Fittingly the common Dwarf is without a home of their own, with only the Kharadron Overlords and Grimnir's Fyreslayers having Holds. The rest of the race are called Dispossessed and dwell with Sigmar or are scattered. Also fittingly, reference to alcohol in AoS is very rare and Dwarfs have apparently replaced their lust for alcohol with a far more obsessive lust for gold.
So remember that while there's evidence of AoS becoming more gender and race inclusive, Dwarf women got Fridged.
Valaya has no impact on any form of gameplay in any Warhammer work outside of Total War: Warhammer where she has minor effect on the Dwarf economy in a few ways as well as the Daughter Of Valaya female Dwarf that can be a companion to any Lord character. Several Rune upgrades are tied to her, but are technically the works of Grungni (unless you count all Runes and Runesmiths as being the product of her literacy).