The actress and her She & Him bandmate M. Ward created new music for the family film - Deschanel tackled the theme tune while the pop couple also recorded So Long, which was played over the end credits of the movie.
But Deschanel admits she was wracked with nerves when movie bosses first approached her about the project.
She tells TheWrap.com, "The tradition of music in Disney animated films is pretty spectacular. But I tried not to think about it, because I might be overwhelmed if I did.
"This was like cracking a code. I had to think, 'How do I accomplish all these things for the movie, how do I tell the story without getting too literal or writing something totally off-topic?'
"But once I did crack the code, it was inspiring. And the movie people pretty much let me do my thing. They were extremely cool about letting me have my creative moment with the song."
Deschanel's dedication to the track has paid off - So Long is on the long list for the coveted Best Song prize at the Academy Awards, which take place next month (Feb12).