It's a great character/power, but here's the thing:
The sickness isn't quite like you seem to think. It doesn't really HIT you really quickly, and it takes approx 2 days to die from it. Also, animals aren't affected. Try this:
She killed the last wolf, but her wounds were so great that she passed out. For the next 48 hours she lay on the forest floor, unable to move. The disease has finally caught up to her, and because of the wolf blood thats been transfered to her own blood, she becomes half wolf.