In the new song "Making Today a Perfect Day," you can hear at the beginning a little bit of "Life's Too Short," a song that did not make it into the final cut of La Reine des neiges (2013).
In the first La Reine des neiges (2013) movie, Anna wakes up Elsa when they were little. In the short film, Elsa does the same routine as Anna.
Frozen Fever is the second short Disney has done after a movie. The first was Le Mariage de Raiponce (2012), which followed Raiponce (2010).
At the beginning of the short, Elsa makes an ice sculpture of herself crying and hugging frozen Anna, which happened at the end of La Reine des neiges (2013).
At first, "Surprise" was a title for the new song in Frozen Fever but the songwriters quickly realized Idina Menzel already had a song with the same title in the musical If/Then.