She actively ruins the experience in my view. During a first run-through she spoils solutions, on subsequent run-throughs she’s just plain boring and repetitve, making her smug countenance even more grating. Makes me wish she blew up in that car along with her parents.
Also, rule number one in story-telling is to show, not tell. This is especially true of video games, which is all about “showing” as it can do so directly and effectively. When we enter the sprawling grounds of a mansion owned by the head of a drug cartel and see armed guards all around, we really DO NOT need some narrator voice literally telling us how dangerous the situation is. Let us get immersed in the experience ourselves and trust us to figure out for ourselves that it is indeed dangerous. Having Diana emphasize it is both a disservice to the player as well as all the people who worked so hard on the level to get a certain atmosphere across.
Sorry for the strong tone but Diana irritates me to no end. And I’m not talking about the character or the voice actor per sé (though in both instances I preferred her earlier versions pre-Absolution, but for instance in the pre-mission briefing videos I think current Diana works quite well), but about Diana as the exponent of hand-holding going on in this game.