The City of Silver Light — Ruth Fox

It's an unusually cold winter, but 15 year old Jake is more concerned with the ice forming in his dad's new relationship, the fact that the girl he likes is dating his best friend, and his elderly neighbour is acting even weirder than usual. Could things get any more confusing? And then on a night of frost and ice, the beautiful ice-girl Cari falls from the sky, cast out of her world and into ours, and Jake finds that things will never be the same again.