Undead and Unfinished (Betsy Taylor Series #9)

Vampire Queen Betsy Taylor is having a tough time getting through the Book of the Dead-until the Devil strikes a bargain. She offers Betsy a chance to finish the cursed (literally!) thing, and finally discover all its mysteries. There's just one catch... Betsy and her half-sister Laura have to go to Hell long enough for Laura to embrace her dark heritage (after a rebellious youth of charity work) and finally make nice with her mother, aka Lucifer. That means interacting with their family's past. In doing so, they're impacting the future in ways they never anticipated. Of course that's what Mother wanted all along. Damn her.