I think parent comment was referring to "Sybil" or something similar (it isn't the only story about DID like this), which was based on a real person, except there's indication her psychiatrist was tricking her into thinking she had multiple personalities and then helping resolve those personalities in order to make money off the story. Pretty much everything about the case is unclear at this point, other than that shady biz was going on everywhere once people realized there was big money to be made.

https://en.wikipedia.org/wiki/Sybil_(Schreiber_book)