Senior (2015)

An outcast weirdo at a Catholic girls' boarding school. She has a special nose. Unlike the kid in The Sixth Sense, the olfactorily gifted girl Mon (Ploychompoo Jannine Weigel) can't see dead people, she smells them. More specifically, she can sniff out the troubled spirits who are still lurking in our realm. Her unique talent leads her to develop a connection with a boy ghost (Bom Phongsakon Tosuwan) who was a student when the place was a business school in the 1980s, before it was a church convent. Together, they investigate a murder that occurred there some 50 years before, when the school was the palace home of a princess, who was found beaten, bloodied and very much dead in her swimming pool. Her gardener took the fall for the death, but there was more to the case than met the eye.

Source: TMDb