[quote=PandaBrady]
...Go on.
[/quote]

She is omnivorous of course, but she also can feed off something else: fear and pain in battle. As she inflicts those emotions upon her enemies during combat, her body magically absorbs some of that emotional energy, thus sustaining her. She would not be aware of it initially as she didn't have to go without food and water before.

Also, as she doesn't care about souls, I'd assume those she kills will drop their souls for someone else to have, right?