I know very little about what the Dusk Monarch is. I believe it is Silver making herself into the monster she believes she is. It could be that Silvia, and the AI, are seperate, but share a form, and the AI part of her adapts to the change in her mindset, making her monstrous, and destructive. I don't know how she even got that name though. Perhaps, she just saw it to be fitting for how a dark ice follows that form.
Whatever is going on with that form, it is extremely dangerous to any life that surrounds it, in game, or not in game. Ice seems to form inside of you, and outside as the room gets supernaturally cold. She cannot be stopped other than by shutting the DS. However, in game, no objects, or power-ups seem to work.
Despite it all, I do not think Silv is a lost cause. From the sound of it, she killed her friends by accident, rather than on purpose. Perhaps, that's why she always hides her true feelings, as whatever she is, her emotions can impact her surroundings, such as temperature. I feel like she is not really a bad person. Am I wrong to say that? I don't know anymore.