Yes, it is common knowledge that Lohan read for the "mean girl" part (Regina George, which went to Rachel McAdams) in one of the greatest teen comedies ever written, but she felt that it would hurt her reputation. Which is ironic, considering her career trajectory after the movie.
Mean Girls is Lohan's peak. It's regarded as her best film, and she's flawless as Cady, the innocent good girl from Africa who gets mixed up with the wrong crowd. It was an undoubtable indication that Lohan was well on her way to a very exciting, award-winning career. But then real life began to interfere with her acting, and her personal business became much more interesting to the general public than her subsequent films. And that's how we got The Canyons. —TA