She won the bronze medal in the women's 200-metre freestyle at the Pan American Games in Santo Domingo, Dominican Republic.

A member of Clube de Regatas do Flamengo swimming team, she also represented her native country at the 2004 Summer Olympics in Athens, Greece.

Throughout her career defended red-black colours of Flamengo, the club of her heart, yet she has been besieged by other swim teams, with far better training structures.

[9] Although these medals won in 2003 Pan have called more attention around her name that year, before heading to Santo Domingo, Mariana represented Brazil in the 2003 World Aquatics Championships, in Barcelona, one of three World Championships that she played, when she reached the semifinal of the 200-metre freestyle, beating the South American record by scoring 2:01.17,[10][11] her best mark in long course throughout her career, and obtained the 15th place overall at the proof.

[15] At Brazil Trophy, in 2004, cemented her status as the best Brazilian in the race, and secured his place in the national team that would go to the Olympic Games in Athens 2004.

[24] In 2007, she saw her dream to represent Brazil in the Pan American Games, held in Rio de Janeiro, her hometown, being frustrated by not getting ratings.