Verity by Colleen Hoover

Lowen Ashleigh is a writer who's offered the opportunity to complete the last three novels of a bestselling book series because the author, Verity Crawford, is unable to do so for medical reasons. When Lowen moves into the Crawford house to go over Verity's notes, Lowen sees that Verity has been left largely unresponsive after a car accident. She also learns that Verity's two twin daughters died in the months preceding Verity's accident. Lowen soon finds her self attracted to Jeremy, Verity's husband, and she also discovers an autobiographical manuscript by Verity, which contains dark secrets about Verity's life.