Translation:In the story, the princess saves the country after having eaten lunch.
This sentence is very complicated. I feels like I'm learning both Norwegian and English at the same time. Killing two bird with one stone
In English I would always say 'after eating lunch' unless I were intent on a literal translation.
In British English, we usually go for the simplest sentences. We might say "The princess saved the country after eating lunch" or "The princess saved the country after lunch". The second alternative does not say the princess ate lunch but it is implied.