In August 1980, Nadine Sine joined the faculty at Lehigh University as an instructor, having just completed course work for the Ph.D. at New York University. Three years later, that degree was granted for her dissertation entitled The evolution of symphonic worlds: Tonality in the symphonies of Gustav Mahler, and she was promoted to the rank of assistant professor. She was tenured in 1989 along with the promotion to associate professor, followed by full professor in 1996. Except for the years 2006-2009, she served as department chair 1992-2018, leading the music department in a period of tremendous growth surrounding the move into the Zoellner Arts Center in 1997. In 2018, she was awarded the Hillman Award for teaching and advancing the interests of the university.
Scholarly activity has centered around the music and culture of the turn of the century; in addition to her work on Mahler, she has presented papers at the national meeting of the American Musicological Society and published articles on Strauss as well as early Schoenberg. In 2003 her entry on Alma Mahler in Women Composers: Music Through the Ages, vol. 7 was published, and in 2004 she delivered a paper on Alma Mahler and Amy Beach at the Seventh International Festival of Women Composers conference at Indiana University of Pennsylvania and Carnegie Mellon. In 2007 she presented a paper on Leonard Bernstein's Mahler at the College Music Society regional conference.
At Lehigh University, Professor Sine teaches the four-semester music history sequence, occasional courses devoted to particular composers (e.g., Bach, Mozart, Beethoven, Mahler), appreciation courses and a freshman seminar on Mozart. She also advises the growing number of music majors and minors. Sine has performed extensively with choral ensembles at the university, in the community, and professionally. For two years she was a DJ on a weekly program of classical music on WDIY-FM, the Lehigh Valley's first public radio station, and she has often written program notes and offered pre-concert lectures for professional ensembles in the state, particularly for visiting orchestras at the Zoellner Arts Center.