In the current game, there’s 4 factions.
There’s the Forces of Order, the Empire, Bretonnia, Dwarfs, High Elves, Wood Elves, and Lizardmen.
There’s the Forces of Chaos, the Daemons, Hordes of Chaos, Beastment, Skaven and Chaos Dwarfs.
There’s the Forces of Destruction, the Greenskins, Dark Elves, and Ogre Kingdoms.
Finally, there’s the Forces of Death, Vampire Counts and the Tomb Kings.
Either way, Genevieve Dieudonné is of the Lahmian bloodline. Even though they’re evil undead, they have watched over mankind for ages. They’ve helped them against the Chaos hordes and even against the Von Carsteins of Sylvania. This isn’t out of the goodness of their hearts though, they just want humans alive because they need them as blood bags. They’ve also done some evil shït as well. But at the end of the day, she saved Karl Franz life and is allowed in the Empire.
Also, from the wiki,
“The sisterhood secretly protect her; despite her status as a third generation rogue with no place amongst the true Lahmians, she is valued for her ability to influence the minds of mortals into softening towards Vampires”