The 23-year-old actress was originally set to team up with her former "Harry Potter" director David Yates for the adaptation of Emma Forrest's memoir a few years ago before production stalled.
While Yates has since dropped out, Watson is still attached to take the lead in the drama, said The Hollywood Reporter.
Gregorini, who co-directed "Tanner Hall", has signed on to direct the project, and the film will now be financially backed by Benaroya Pictures instead of Warner Bros.
She then embarks upon a course of therapy with a psychiatrist who is dealing with his own terminal cancer.
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It has not yet known whether "The Hunger Games" actor Stanley Tucci is still on board to star as the shrink as previously reported.
Author and journalist Forrest has written the screenplay based on her own book, and Alison Owen and Michael Benaroya will produce.
Filming is expected to start this November in New York City.