 Olivera made her breakthrough at the junior level in 1994 when she won the 10,000 metres gold and 3000 metres bronze medals at the South American Junior Championships in Athletics.The following year she upgraded to a gold and a silver medal at the Pan American Junior Championships, before going on to complete a hat-trick of medals at the South American Junior Championships – she secured a 10,000 m and 3000 m double and also won the 1500 metres silver behind Bertha Sánchez.Olivera is a two-time winner of the South American Cross Country Championships, having beaten all comers in both the long and short races in 1999.