D.W.
It's because she is just 1! Very, very common occurrence right about the time they turn 1. I learned this when my super sleeping champ started suddenly waking right around the time he turned 1. They become much more aware of the outside world, they wake in the night and don't want to miss out. Just provide gentle comfort to get her back to sleep-tell her it's still night night, etc, offer something to drink perhaps or nurse her if she nurses. It will pass. Just keep up your normal routine. Letting her cry it out isn't going to help at all.