A ramp and commercial model, she was crowned Mutya ng Pilipinas in 1977 and won Fourth Runner-up in the Miss Asia Pageant that same year.

Díaz began a relationship with musician Hajji Alejandro, and together they emigrated to Los Angeles, California, where they operated a small restaurant along Melrose Avenue.

Diaz, similar to her first husband Hajji Alejandro, was a supporter of former President Ferdinand Marcos, even after his deposition in the People Power Revolution.

When the cancer cells returned in May 2000, Rio travelled back to Stanford for an eight-hour surgical procedure and another round of chemotherapy sessions.

Six years after the original diagnosis, Díaz died on October 4, 2004, at Seton Medical Center in Daly City, California, at the age of 45.