My bet: she had some sort of supernatural experience (to prove spirits and etc are real) and then she learned her dad is an exorcist, so her smile is a "I know your secret, lol" kind of expression. Next chapter will probably be a flashback showing the what actually happened. She's probably the newest member of the snake cult or something, since "Yasaka" can leave the area more easily than Dara can. (Although the way the chapter was translated was a smidge confusing this time, she did end up going on her trip anyways, right? It was just that her dad couldn't join her?)