Del Rosario attended the University of Puerto Rico (UPR), Río Piedras campus, from 1931 until 1935, where she earned a bachelor’s degree in physical sciences. After teaching high school for two years, she traveled to the University of Chicago in 1940 to continue graduate studies. There she worked with Arthur J. Dempster in a thesis titled “The Relative Abundance of Lithium Isotopes”. After obtaining a master’s degree, she returned to Puerto Rico and continued teaching in high school before joining the University of Puerto Rico as a professor of physics in 1943. In 1944, she went back to Chicago to continue doctoral studies under the guidance of Samuel K. Allison, at that time Director of the Institute for Nuclear Studies (renamed as Enrico Fermi Institute for Nuclear Studies in 1955). While in Chicago, she was also a student of Arthur H. Compton, and Enrico Fermi. In 1948 she graduated with the thesis “Use of electron multiplier tube as a new technique in disintegration experiment”.