She assumed that an angel-or former angel-would know that better than anyone. She also assumed that it was simply flattered aimed at... what, exactly? Getting information, or was there another motive in there? Perhaps that spoke to just how much bad luck the Winchesters had had with angels in the past that she was automatically suspicious.
"I suppose that confirms that you're from a different reality though," she said easily.
It wasn't conceit that caused her to believe that every angel knew her family's name. It was the fact that the dicks with wings couldn't keep their hands out of her family's business. Even decades after the apocalypse they'd wanted had been averted and was over and done. Even then, they were still bringing Mary and her sister back to the past in an attempt to save her parents, for whatever reason Heaven felt that her family's destiny mattered more than others'. Not that she would ever complain about the chance to save her blood, but she knew how many lives had been lost along the way, both in her life and in her parents' lives. She knew how many people Heaven wouldn't lift a finger to save. And like every Winchester, she couldn't help but resent the angels for ignoring others while focusing on her family. For failing to be equal opportunity saviors.