Blood Vice, book 5Angela Roquet

With her home and heart in ruins, Jenna is none too keen on the idea of helping the Duke of House Lilith—the man she holds responsible for everything wrong in her life. But when the Vampiric High Council summons Ursula, Duchess of House Lilith and Jenna’s unsuspecting grandsire, to a trial where she's to stand accused of murdering her sire and abandoning her depraved scions, the duke is eager to strike a deal. If Jenna helps him protect Ursula, he will keep her darkest secret and put in a good word with the adoptive sire the queen assigns to her. Oh, and return her guns—provided she doesn’t use them on him.