The song "I Will Survive" plays in Allison's head until she finds Isabel's iPod. Originally, the producers were thinking of having the song play throughout the entire episode (thank goodness they changed their minds).
The song "I Will Survive" is a popular song released in 1978 written by Freddie Perrin and Dino Fekaria but sung by Gloria Gaynor.
The song in question is Gloria Gaynor's "I Will Survive" which (apart from the opening titles) plays repeatedly for the first six minutes of the episode. This includes in a memorable opening sequence in which Patricia Arquette lipsyncs to the song in an animated background.