The teenager has taken a break from her acting career while she tours Europe and the US with her band The Pretty Reckless and said she does enjoy acting but not as much as her music.
She said to OK!: 'I've been writing songs since I was five. Acting is something I was put into and I enjoy it, but it's very much a job to me, whereas music is something I couldn't live without.
'I couldn't live without it. I would be dead without music.'
Momsen has no hard feelings about her departure from the show.
She added: 'I have to really thank them. I can't be in London and filming the show in New York. I mean, you just can't.
'I have to thank them for being very supportive of the band and the record and allowing me to tour and support it.'