In a recent interview, the interviewer asked Shin Hye why she has not appeared on the trailer of the movie. Shin Hye admitted that her appearance in the movie is not that long. Here's the link.
link
Here's the translated part courtesy of google translate:
Q: Not appear in the trailer was not that fine, somehow Shinhye Mr. hidden card character, right?
PSH: Grown daughter of equipment.
Appeared amount is not a lot, it's literally the gift of '7 Room Number 'figures. People probably bosimyeon'll be surprised (laughs). Too laughing rings can be so sad, made me laugh ... It's a movie that contains everything.
Well. if it's okay with her then I won't complain. It seems like she accepted the role because of the character and to be able to work with veteran and top actors like Ryu Seung Ryong. I guess she really wants to focus on her studies first rather than tire herself out in doing nonstop dramas or movies every year. That seems like a really good decision and I salute her for setting limits and honoring her priorities.