Mentioning Oliver even in an indirect way put a foul taste in Hermione's mouth. She didn't want Rodolphus to even think about her son. And she couldn't deny that the reminder of what a shit mum she was always stung. If she had the opportunity in the future, she would try her hardest to be better. Oliver deserved more. It was a shame for him that he'd been cursed with her for a mother. Maybe if he'd been a terror and a nasty kid she might've felt better about the circumstances. Knowing what a sweet, loving young man he was growing into made it all so much worse.