She never told Harry about her demon friends - he was too Light aligned. But she did share the secret of her own talent in being able to talk with birds with him, in solidarity. He was delighted to have that camaraderie of the shared secret that she too could talk to an animal, and she translated many sweet conversations with Hedwig for him. She didn’t tell him about her ability’s origin as a demonic gift, however. It was the same method by which Salazar Slytherin had once gained the ability to talk to serpents for himself and all his descendants. She did encourage Harry to be proud of his obvious descent from such an esteemed wizard – it was a noble line. Unfortunately, it was an argument that worked better on Slytherins than Gryffindors.