Who is the only Disney princess to appear in a Pixar film?

The only Disney princess to appear in a Pixar film is Merida from "Brave." Released in 2012, "Brave" features Merida as its main character, showcasing her journey of self-discovery and her desire to change her fate. As a Pixar film, "Brave" is distinct from the traditional Disney princess franchise, highlighting Merida's adventurous spirit and independence.