She's capable of flinging a very powerful area of effect spell, is immune or resistant to every form of Destruction magic, and quickly regenerates lost Health, Magicka, and Fatigue. Once you are able to create customized spells, combining high-intensity, short-duration 'Weakness to _' spells with damage of that element is an easy way to deal massive damage relatively early. Additionally, there is a ' backpath' method to beating the main quest that only requires two particular NPCs to be alive, but again, you can also kill them to render even this method unwinnable.
This can actually render the main quest unbeatable if you kill a plot-important NPC (the game does pop up a warning message telling you to reload a saved game if you do kill one). Every NPC in the game can be killed if you choose/are able to do so. Damage Discrimination: Averted for NPCs.
