The singer, who is releasing a greatest hits compilation and single 'Raise Your Glass' next month to mark ten years in the business, said that her success is a "huge accomplishment" because she refused to become an "endorsement girl".
"The reason I wrote 'Raise Your Glass' is because it's a celebration of being an underdog," she told In Demand.
"Instead of becoming a cover girl and endorsement girl and a popular girl and having number ones - I mean I've had one number one in my entire career - I just hit the road and pounded the pavement and became a touring artist.
"That has been a huge accomplishment for me. You don't have to be popular when you're a touring artist, you just have to be good. This album is a celebration and a thank you to everybody for hanging out with me for so long."
She confessed that the retrospective LP is called Greatest Hits...So Far because "I still feel like 17 and I haven't hit my halfway mark".
The 'Sober' star also hinted at rumours of an acoustic album in the future, but was unsure how it would sound.
She said: "I'm going to do [an acoustic album]. I'm definitely going to do that. It's only going to come out if it's amazing, it could be complete crap."
Greatest Hits...So Far is out November 15.