Hitman 2 (2018) spoilers
So, I think it’s safe to assume that Diana doesn’t know that the deaths of her parents was the work of Agent 47 and Lucas Grey. I don’t think she’d take it well at all. The reason I say that is because in Agent 47: Birth of the Hitman #1, she seeks help to kill people, presumably people from Blue Seed Pharma, the company responsible for her brother’s death. I think it would be safe to say she would turn of 47 if she ever found out that he was involved in the death of her parents.