She’d figured out rather early on into the Horcrux hunt that Harry himself had a piece of Voldemort living inside him and that he would have to die for Voldemort to be defeated. It was clear that Dumbledore had known, making him despicable as he’d obviously had Harry raised just to be slaughtered at the right time. She had neglected telling him all this because she’d wanted to spare him the burden of the ugly truth.