There was a backing track but she was not lip syncing to pre-recorded vocals. WTF, people can be so dumb. If you listen closely, you can tell when the backing track kicks in, in the sustained high notes which she also sings (which is why you hear two voices). And she doesn't need the backing track at all, the vocals was near-perfect.

I have to agree with everyone else though that she is wasting immense talent on average material. The song is not bad, but her material is just not on par with her talent. And it shows. A LOT.