Lara only trusts close family for the important public jobs, especially after Madrigal's & Madeline's treacheries in White Night & Turn Coat, respectively, which means sisters and nieces. And Harry might have grown up a bunch from the leering in the early books (especially given that he now has a daughter and avuncular relationships to a few woman-shaped people, like Molly & Ivy), but he's still Harry, and he's gonna see the she-vampires first. He's not going to pay attention to the build and grace of a man until he needs to, or is otherwise made aware.