Arenas was born Rose Marie Bosch Jimenez in 1938 in Malasiqui, Pangasinan. Her parents were Alfredo Jimenez, an accountant at the Bureau of Internal Revenue (BIR) and a member of a modestly rich family from Makati; and Remedios Bosch, an opera singer and a music professor at the University of the East (UE). Her father was known as the disciplinarian in the family while her mother influenced her love for charity work, culture, and the performing arts. Due in part to her well-connected mother who sang in the prestigious opera galas in Manila and abroad, Arenas was exposed early to Manila's high society.