She taught in the Spanish Department on the Rio Piedras campus.

Arrillaga received her BS in English in 1961 from St. Louis University, her MA in Spanish from the School of Education at New York University, New York, in 1966, and a PhD from University of Puerto Rico in 1987, on the subject of Latin American and Puerto Rican literature and Women's Studies.

From 1970 to 1971 she was an instructor of art and music of Puerto Rico, New York City Technical College, Brooklyn, New York.

From 1973 to 2001 she was a Spanish Professor, College of General Studies, University of Puerto Rico, Río Piedras Campus.

In 1993–94 she was a visiting professor, York College, Queens (CUNY), teaching Women's Literature and Creative Writing.