So, apparently California is a song she did collaborating with a band (consisting of Miles Kanes and Alex Turtner) which was part of an album she did with them and which probably will never be released. Which is such a shame because the song is amazing and one of my favorites on the album.
The amount of music she works on and we have no idea..
Source: https://www.youtube.com/channel/UCkyyfaPlowG6oqODqFknJbw/community?lb=UgxFvZlYGPXx9iVWajd4AaABCQ