Genevieve Sandrine du Pointe du Lac Dieudonné
A character of a series of books written in the ye olde days of WHFB, by Jack Yeovil, more widely known as the film critic/horror buff Kim Newman. A very old (older than most adult elves) Wuxia French Kung Fu master barmaid vampiress blessed by the God Conan of Barbariankind in the Warhammer Fantasy Battles universe. I swear I'm not making this shit up.
A long time ago, in Parravon there lived a young Bretonnian (French) girl. Her father was a servant to the local knightly lord. Then a big meanie invaded, killing fuckloads of people and executing all the nobles while plundering the province. Poor little Genevieve was left on the streets of a mostly depopulated dukedom, and at the age of 16 a pedovampire named Chandagnac found her and made her one of his wives. Chandagnac himself was a servant to Lady Melissa d'Acques, a very prestigious cougar of the Lahmian Bloodline.
Chandagnac was shortly after hunted down by priests of Ulric, as he was far too dim-witted and far too eccentric to stay hidden. Now left with nobody in the world but with a bloodlust and superhuman powers, Genevieve went east.
She spent some time in Araby (the Middle East), during the crusades between them and her people. Eventually she proceeded through the Warhammer Silk Road and ended up in Cathay, AKA Warhammer China. She became a trader between Cathay and Nippon (Japan), making her one of the few beings to have ever been to Nippon.
At some point she met a master monk named Master Po (showing GW being creative as always). She spend thirty years with him learning to control her blood lust to the point she required very little to survive and both telling stories to him, as well as learning quite a bit about the cultures Cathay has met. Eventually Master Po went on to teach important Cathayan generals, but that's not important at all since GW has never bothered making Cathay relevant.
Genevieve traveled to the Empire soon after, where she came out of the closet as a vampire. Somehow this was acceptable in her case, and she mingled in high society until she became bored and frustrated with the pompous nobility (Magnus the Pious, one of the greatest Emperors of the Empire, feeling her up as a greeting probably contributed). She slipped into the lower class, and ended up working as a barmaid in Altdorf for several decades. During this time, she helped catch a Jack The Ripper style figure and became even more disillusioned by the arrogant and childish nobles.
Eventually she was found by the Elector Count Oswald von Konigswald who paid her to join him in his quest to kill Drachenfels. Genevieve spent most of her time killing the greenskins/Daemons/Undead in the corridors while Oswald snuck in to kill Drach. After their victory, Genevieve returned to her inn and purchased it.
Decades later, Oswald invited her along with the highest nobility of the time to a play about "his" defeat of Drachenfels. There she met Karl Franz, whom she took a liking to, and the actress playing her, whom she very much hated. Drachenfels returned to life during the play, and in order to fight him, Sigmar granted his blessing to Genevieve and to the play's director Detlef Sierck. Genevieve fed on Drachenfels to survive wounds during the battle, and in doing so read his mind and saw the extent of his evil deeds as well as how eternal he was. After the defeat of Drachenfels, Genevieve and Detlef fell in love.
They returned to her inn, where he continued to write plays known the world over from Ulthuan to Lustria (who knew the Slann were patrons of the arts? More likely it was referring to the human settlements there such as the town of Skeggi). She bankrolled his productions.
Genevieve MAY have had a fleeting unnamed cameo in the End Times lorebook: Nagash. One of the short lore pieces goes into detail about a mysterious meeting that Balthasar Gelt has with an unnamed woman cloaked in shadow and who basically feeds him the idea and plans for the Auric Bastion to stop the Chaos invasion. This is later revealed to be the minion of Queen Neferata, the top Lahmian vampire, as the Vampires have a vested interest in the world continuing and not being destroyed.
The kicker is that in this meeting Gelt notes that the unnamed girl sounds like a Bretonnian from Paravon or Montfort, is very young and drinks a ruby liquid from a goblet. She also states she does not like her female master. Considering that Genevieve is a notably free-willed and independent Lahmian Vampire from Parravon and that otherwise all Lahmians revere Neferata, this seems like a suggestive nod from GW to the audience as to who this woman is, though it looks like coincidental evidence, but pretty cool nonetheless. As to WHY Genevieve may want to work for her progenitor Neferata considering she has ignored more malevolent vampires in the past, she could just have an alignment of interests with her in not wanting to see the world ended or it's her way of serving Nagash so he doesn't set her brain on fire inside her skull (like he did with all Vampires who refused to serve him, such as Zacharias The Everliving) since as a Vampire Genevieve would certainly have felt Nagash's return.
During Karl's ascendance into God Emperorhood, a wave of holy magic radiated through her home city of Altdorf and burned away the filth of generations (as well as all daemons and undead). She likely survived despite her undead nature, given that Sigmar had empowered her with holy light in a similar (although smaller scale) way before.
As Drachenfels in End Times has lost all his memories including his own name, when Genevieve bit him she didn't only get his congealed blood; she stole his memories as well. Nagash has promised to return them to him if he serves as a servant, meaning Genevieve may possibly be in danger from Nagash (if she dies, some on /tg/ have sworn to riot and destroy Games Workshop headquarters once and for all).
The Drachenfels and Genevieve stories rely on canon that has since been retconned, and any discussion about either will usually start an argument over the canonicity of the story. To get a picture of how retconned it is, the Bretonnia of her stories is modelled on the pre-French revolution version that was written over YEARS ago. The fact she's a very popular character in the Warhammer Fantasy communities, and her books are generally regarded as being very well written makes those discussions particularly heated.
Almost every source cites the fact that Vampires are universally reviled in the Warhammer Fantasy universe, and in the Empire being or working with the Undead is a heresy as grave as working with Chaos. Despite this Genevieve is openly a vampire and mingles throughout Empire society. She only receives unease from others rather than being chased with pitchforks, and the Witch Hunters of the Empire would normally not hesitate to FWIP anyone regardless of their position. For this the only logical explanation is that she has had the approval of three Emperors, who's authority even the Witch Hunters must obey. The fact that somehow Sigmar's light didn't disintegrate her but instead empowered her is also questionable, but at least with the acceptance that it DID work must give her some credit (then again, in Mordheim the Sigmarite Witch Hunters spent as much time killing heretics as they did the other Sigmarites due to the fact that prophesies from Sigmar are still prophesies, and magic is HERESY).
However, the books infer Genevieve's vampirism is an open secret, as she was chased more than once by angry mobs when her vampirism was discovered but managed to sneak away. Furthermore, she had a vampire support group (of other vampires) who let her know if any Witch Hunters were nearby, in which case she'd keep a low profile. It also helped that she only fed on willing people.
Drachenfels himself is full of canon plot holes, but that can be seen and argued on his own page.
The fact that in the End Times event Drachenfels is canon suggests however that Genevieve is as well. Then again, in End Times everything, well, ended.
That being said, it's been shown through Nagash that many Undead survived (at the very least his Mortarchs and their mounts) so she may have persisted into Age of Sigmar as well, and it's not completely impossible she could be a Sigmarine, as even the undead are part of the ranks. Of course, Drach would have as well.
On the Tabletop
Genevieve, thanks to her globe-trotting lifestyle, could be fluffed into most Order armies. Of course Empire and Bretonnia armies work best, as does the player who fields a homemade Cathayan army. For a model the Bretonnian Damsels or the Vampire maidens off the Coven Throne model work best. If using End Times rules, then a wizard in Lore of Undeath works as well.