Bortnik attended the University of Buenos Aires from 1956 to 1958 and from 1961 to 1964. She also attended schools of theatre and film.
Bortnik started her career as a TV-screenwriter in 1971. She co-wrote with débutant director Sergio Renán the screenplay for The Truce (1974), based on the eponymous novel by Mario Benedetti. That year, Bortnik also co-wrote Una mujer, directed by Juan José Stagnaro. After a three-year break, Bortnik worked one more time with Renán in writing a screenplay in 1977 for Haroldo Conti's novel, Crecer de golpe. She then co-wrote La isla (1979) with director Alejandro Doria.
In 1985, Bortnik co-wrote with writer-director Luis Puenzo a screenplay for a film about the Argentine Dirty War, which had recently ceased. That same year, she co-wrote Pobre mariposa with director Raúl de la Torre. In 1989, Bortnik helped Puenzo write the screenplay for Carlos Fuentes' novel Old Gringo, a United States production; the only non-Argentine project in which Bortnik was involved.
During the 90s, Bortnik worked strictly with newcomer writer/director Marcelo Piñeyro, who had served as executive producer to La historia oficial. Bortnik helped Piñeyro write the screenplays for Tango feroz: la leyenda de Tanguito (1993), Caballos salvajes (1995) and Cenizas del Paraíso (1997), a loose trilogy. She renewed her working relationship with Sergio Renán, co-writing La soledad era esto (2002).
Bortnik's last job was as an occasional writer for the series Vientos de agua in 2006.
Bortnik was a member of the General Association of Authors of Argentina.