Hilary Duff turned down her role as Kelsey Peters because the series was set to be shot in New York, and she lives in Los Angeles. Darren Star called her and said that the role was hers and that he wouldn't take "no" as an answer, so she accepted it.
Sutton Foster (Liza Miller) admitted that she went to Hilary Duff (Kelsey Peters) for fashion inspiration during the first season.
Hilary Duff was pregnant with her daughter, and third child, Mae, during the filming of Season 7 which they tried to cover up with her clothing.
Debi Mazar (Maggie) said that her daughters grew up watching Lizzie McGuire (2001). So, she knew Hilary Duff (Kelsey Peters) from her days on the Disney Channel.