She didn't know what she was doing in Tokyo. She had booked herself a flight, packed her bags in an orderly fashion and organised her documents. She had carefully thought through the travel arrangements, just not the 'travel' component, you know, the 'life' part.
I mean, most people go on a trip for a purpose. On those little outgoing/incoming passenger cards you have to tick a box: leisure, business, education, visiting family...
She had no real reason for flying to Japan. So she ticked 'business'. If she didn't know what she was doing there, she intended on finding out and that could be hard work. Yes- definitely 'business'.