This is not actually an integral part of the romance, so it doesn't matter if she doesn't get kidnapped. But it should happen as long as the romance is active (I think?), just go to the graveyard and check, she'll be kidnapped as soon as you get there, if not load your autosave. There's quite a few dialogues left before you sleep with her; the romance works on realtime so just leave your game for a while (an hour if you don't have the improved romance file, half an hour if you do) and when you come back there should be another dialogue.
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Goddess and Sorceress of the HADB, and her sidekick Pink