[She has to think of a way to say this as delicately as possible. This isn't Karkat, she can't just talk over him and sweep aside his objections because he's ridiculous anyway and she can get away with it and she knows she's right. Laura does not have the benefit of that understanding.]

You can try, yes. I don't mean that as a slight on your abilities. But it's not really possible for you take responsibility for everything that happens to everyone. There will be things you can't be there for, things you can prevent and things you can't, either because they have to go that way or there's a limit to how much you can do, how many choices you can make to insure an possible outcome. I know that probably isn't very easy to hear! But I think if you spend so much time worrying about what you could have done, even if it's understandable, it doesn't benefit anybody. Nobody would blame you for not being there but yourself.

[Time traveler logic. Of course this doesn't apply to her; in theory she could probably make anything happen, but there would be consequences and doomed timelines and she knows, sometimes, people die, and there's nothing to be done, and it's not easy.]