Complex sentence: Justice has done advertisements for companies such as Ralph Lauren, Gap, and Guess, and has appeared in national commercials for Mervyn's, Peanut Butter Toast Crunch, and Ovaltine.
Split into simpler sentences: Justice has done commercials for companies such as Ralph Lauren, Gap, and Guess. She appeared in national commercials for Mervyn's, Peanut Butter Toast Crunch, and Ovaltine.