Is imperial princess based more on the anime than the manga/light novel? It seems to be the case as the way being X is portrayed, the date of her death, and the UK being called Albion instead of the United Kingdom make it seem as though it follows the anime version more.
Although what I said earlier it seems as though Tanya's character is based far more on her manga/light novel version with her being less 'evil' and showing a bit more of her childish elements they threw away in the anime.