Born into a humble family, Arnal Yarza's father was Luis Arnal Foz, a laborer from Zaragoza who later repaired pianos. Her mother, Vicenta Yarza Marquina, of Brea (Zaragoza), was a housewife. After the death of her parents, she had the responsibility of taking care of her two younger siblings. Her sister Pilar was a pianist who studied in Paris and gave concerts in the Teatro Real de Madrid. Her brother Pablo died young, but had a short career as a professor of Physics and Chemistry at the Consejo Superior de Investigaciones Científicas (CSIC).
Jenara's vocation lead her to her teacher training studies at the Escuela de Zaragoza and to a degree in Elementary Education (primary school teaching) on December 3, 1921. Her desire for learning impelled her to continue her studies at the School of Sciences at the University of Zaragoza in the realm of Chemical Sciences, first as a non-matriculated student in 1922–23. Later she continued her studies as a matriculated student, and received high grades and honors in all of her classes. She received her graduate degree from the University of Zaragoza on March 12, 1927.
She defended her doctoral thesis on October 6, 1929, and obtained her Ph.D. in chemistry from the Faculty of Sciences of the University of Zaragoza on December 13, 1929. Her doctoral thesis was titled Estudio potenciométrico del ácido hipocloroso y de sus sales ("Potentiometric study of hypochlorous acid and its salts ”). Thus, Arnal Yarza became the first woman to obtain a doctorate in Chemical Sciences in Spain, later followed by the researchers  y .