Translation:She wants to explain that in her book.
All feminine nouns can be inflected as though they were masculine:
ei bok - boka
en bok - boken
Both, it and that are accepted on our end. It's possible there was another error. Did you, perhaps, report it?
This is a special one for the Dutch, where "verklaren" would be used both as 'to clarify' and 'to declare'. I find that in Norwegian as in English they are two totally different words: å forklåre and å erklære