Shelly, who also wrote and co-starred in the slice-of-life comedy, was murdered last fall.
A hit at this year's Sundance Film Festival, "Waitress" is set to open in the United States on May 2.
"It's incredibly bittersweet," actress Cheryl Hines recently told UPI.
"This is such a happy time because this movie is so beautiful and it's very exciting that people are noticing that ... and taking something away from this movie and, at the same time, Adrienne should be right here and it's not fair," Hines explained.
Actor Nathan Fillion said he's certain Shelly knew she was working a great project.
"I wish she could be here to hear people tell her and to see for herself how she has affected them," Fillion said. "What should have been one more piece in a long line of beautiful works has become a legacy and I'm very happy to have been a part of that."