It's one that just seems to come out of nowhere. I can remember nowhere in the books where Harry associates his mother with the Black Court. He think she was involved with LR, Nic and the Denarians, Demons like Chauncy, Fae, dark wizards like Justin and Rampires through Bianca but never the Black court that I can recall. I can see him believing that she knows somethin about outsiders as Justin and LR have both associated with them.