The sequel may already have its “Let It Go.”“We have a new song that I think is an evolution,” Jennifer Lee, co-director of the first and second films, told Variety on Monday at thepremiere in L.A. “It’s its own song…Bobby [Lopez] and Kristen [Anderson-Lopez] just delivered it three weeks ago. We’ve been working with them for two years and this song just came in and I love it.”Lee, who is co-writing the follow-up withscreenwriter Allison Schroeder , said the song is one of four already chosen for the movie. “We have three more to go,” she said.