Dr. Moriarty works better as a planeswalker, or rather, as an anti-planeswalker. That's what she is, but there was no way to put enough text in there for that. She is convinced that the planeswalkers are causing a crisis on every world in the multi-verse, and that the only way to stop it from worsening is to stop them. As their power, and travel, increases, so too does the damage they cause and the ripple effects all across the multi-verse.
To make it easy for you, it's like she's the first to discover climate change, and its source, and now she has to stop it or die trying.