From Janet's facebook page:
Q: Is it true that Katherine Heigl will portray Stephanie on the big screen in One For the Money? How much of a say did Janet have?
A: Yes, Katherine Heigl is now the actress attached to the One For the Money movie project. Prior to Heigl it was Reese Witherspoon, and before her it was Jennifer Lopez. Janet sold the rights to One For the Money in 1993, before the book was even on the shelves. We're very excited about the movie possibly going into production after all these years. Like most authors who have had a novel bought to be made into a movie, Janet has no say, or influence, when it comes to casting or the script.