Film Theory: Split Is More Than A Standalone Sequel To Unbreakable...
4. Ghostly Encounters
The doctor herself could be argued as an advocate for mental health anomalies causing these powers, or sixth senses, during one scene where she’s watching television with an elderly woman. As the theory suggests, this strange scene to include could be done to indicate Fletcher spending time with the undead herself - as the lady is unable to complete physical tasks on her own with any sort of ease.
Perhaps, by some stretch, it’s because she isn’t part of our dimension.
Fletcher’s own passion for helping those with DID, no matter how controversial it appears to those around her, would be explained by this ability that isn’t openly discussed - maybe because in the world the director has created, there is no need, or it's still a taboo topic even if it's known all the same.
Shyamalan himself claims that the beginning of a shared universe happened with the release of Unbreakable in 2000, the next film after The Sixth Sense, so it makes sense that this would be the first iteration that would be able to link his varying works.
“I want to make a final movie to finish the story of that movie and this movie, then a final conversation of that would be great.” Shyamalan told Yahoo! News. “The Shyamalanverse began with Unbreakable then… It began there, then we’ll see. I have an outline.”