One of the interesting things about Montoya for me is her sense of chivalric martyrdom; she (much like Helena before her) figures she's damned anyway, so she might as well be the one who does the ugly, horrible shit that needs doing, so that nobody else has to. Which is at once both Dianalike and very not Dianalike, since Renee came to that from a place of self-hatred and worthlessness, while Diana sees it as a difficult and important duty obligated her by her upbringing and strength. For most heroes, looking at something and knowing "I'll have a hard time living with myself if I do this" means "it's wrong to do this"; for Diana, though, she knows it's not her job to feel good about herself, it's her job to do what's right. It's that difference in attitude - "I do this because it's bad, like me," versus "I do this because it's important, and I can take it" - that allows Diana the clarity Renee doesn't have, and makes her trustworthy with those decisions even when (as in the Max case, frex) her own emotional involvement, even desire for revenge, is a factor.