The socialite-turned-actress was announced as the lead in Dogs in Pocketbooks, a satire about a troubled young star which screenwriter Charles Casillo has suggested was inspired by the Mean Girls star.
But Hearst, who recently ditched her trademark blonde look, has denied the casting news, explaining she adopted her new auburn hairstyle for a modelling job - and not to look like Lohan for the role.
In a series of messages posted on her Twitter.com page, she writes, "Just so we are all clear... My hair is red because I am the new face of Schwarzkopf Color. I am a model. I dyed my hair to front the campaign.
"As for any theatrical roles I am currently filming Two Jacks directed by Bernard Rose. My next project is Catwalk by Tony Hickox. Thank you all for your messages of encouragement during my transition to acting. I truly love and appreciate it. At this time I am not officially signed onto any other projects."
Casillo has since clarified that the character was inspired by a number of stars besides Lohan - including Marilyn Monroe and Britney Spears - after the actress' mother threatened legal action to halt production.