The Melburnian moved to Spain after falling in love with a Sevillian and the couple now lives in Barcelona.
Brennan took the unexpected turn in her career by replacing Eirian James at Operación Triunfo in May.
"They were looking for an English teacher who also knew music and I thought I fit the role. I sent them a video introducing myself in Spanish and English and they offered me the job!," she told SBS Spanish.
Operación Triunfo, which began airing in 2001, brings together a group of contestants in a musical academy, where they train and demonstrate their singing abilities.
The program has served as a platform to select Spain’s representative for the in previous years.
Brennan considers her job “very interesting" and identifies with the difficulties of “singing in a language that is not your own".
Operación Triunfo contestants Amaia and Alfred representing Spain at the 63rd Eurovision Song Contest in 2018. Source: AAP
She teaches Operación Triunfo contestants how to pronounce English words and their meanings, and where to emphasise them when they sing their songs.
She finds that Spanish-speakers usually have difficulties with pronouns, for example, they confuse “he” and “she”, as well as the sound of the "Y" and "G" followed by the "U", as well as prepositions.
But Brennan admits she has her own dificulties whn speaking Spanish.
She laughs when she recalls that she once said the word "foreskin" instead of "precipice" when speaking with an aunt of her boyfriend, although she is proud to be able to pronounce the Spanish "R" after several years.
‘More empathy’ for immigrants
She arrived with her boyfriend in Barcelona, a city that she admires for its architecture and multiculturalism, without friends or family.
"It is difficult to move to another country, start from scratch, without knowing anyone," she says, adding that it is difficult "to meet people and make real friends" at first.
Her experience as an immigrant in Spain changed her perceptions about immigration in Australia, the country where she taught English at the Refugee Resource Centre (ASCR).
For her, being an immigrant "changes your perspective".
"Now that I am in their shoes, I have more empathy and I identify with them more," she says.
She holds a degree in Hispanic and linguistic philology and a diploma in English teaching from the International House in Buenos Aires, Argentina.
In addition to being a singer-songwriter, she also plays the guitar and piano.
