"I thought, 'you're not happy and if you're not happy, you need to find a way to be happy.' I kind of came to a personal crossroads," she recalls.
"I was loving being on stage and I was loving being a musician, but the classical cross-over - I just didn't love it any more.
I know that might sound a bit harsh, and there are so many wonderful classical cross-over fans out there, but it just wasn't in my heart. I was standing up there on stage and I kind of felt it was disingenuous, like I was pedalling something I didn't really believe in any more."
And so the young singer started to focus her energies on a new genre and set about writing new tunes tinged with pop.
"My poor, poor manager had to listen to a number of rubbish songs to start with," she laughs, referring to Sydney-based Vibica Auld from Modest! Management who also looks after pop acts One Direction, Little Mix and Olly Murs. "I'd obviously been writing songs since I was a little girl but it took a while to sink into it, and when I did, it was surprising and fascinating."
Marvelly isn't giving too much away about her full-length album, due out mid year. But she says it's essentially a pop album and that Generation Young is a good indication of the new direction she's taken.
And that's a good sign. Because Generation Young has all the hallmarks of a pop hit. There is the slow build up to the soaring catchy-as-hell chorus, the empowering lyrics, and of course, flawless vocals from one of New Zealand's purest voices.
For Marvelly, it was important she put her best foot forward. And that meant releasing a big song that stood her apart from her former self, but one not so radical that fans of her previous work would throw up their arms in disgust. Although she admits, that's possible, too.
"I hope that they understand that I just had to be me. I wasn't really doing them or myself any favours carrying on down a road that just didn't really fit me.
"And you know, I've been so lucky. I've had some great fans and I really do hope they come along for the journey. Perhaps I can be the one pop artist that they like."
Marvelly also has no idea how the industry will react to her new sound - whether it will get radio play; whether she can compete with the big international acts like Katy Perry, Taylor Swift and Miley Cyrus.
But what matters, is that she has been brave enough to take this leap of faith and most importantly, she's happy.
"I can't control what the reaction is going to be. But it's totally me and it's the start of me being able to be the artist I want to be and write the music I want to write."
Lizzie Marvelly's new song Generation Young will be available on iTunes on January 10. She will be performing at Rotorua's Lakeside Concert on February 22.