She noticed the ticket was one-way only.
Japanese public security must have told her in no uncertain terms “No, Hikita san, you are NOT going to Pyongyang. You are NOT going to humor that dynastic family and embarrass Japan at the same time. Not until they come completely clean on the various fellow countrymen of yours they still hold as kidnapped victims for low over 30 years now in some cases.” I can just envision her being called into the Prime Minister’s office and given the riot act over that and told her passport would be seized upon reentry, and told to shut up about it.