[1] Brennan made her senior Australian National Championship debut in 2007, having missed 2004, 2005 and 2006 because of injury.

[1] At the 2007 national championships, she finished third in the floor, fourth in the balance beam, eighth in the all around, 12th in the uneven bars, and sixteenth in the vault.

In 2012, she finished first in the all around, third in the balance beam and floor, sixth in the uneven bars and eighth in the vault.

[1] At the 2012 Gymnix International, she finished second in the floor, third in the all around and balance beam, eighth in the vault and tied for seventeenth in the uneven bars.

[9][10] At the same time, she was one of three Australian female gymnasts who were confirmed to be going to the Games alongside Lauren Mitchell and Emily Little.

[12] Her Olympic training preparations included learning how to deal with flash photography with strobe lighting used at practice and being exposed to distracting noises.

[7][13] Brennan qualified in 28th place for the individual all-around final with a score of 54.232 on 29 July, contributing to the Australian team's tenth-place finish during qualification.