I heard of her in November 2008, she had a lot of hype surrounding her for those who were interested. I know her first few releases didn't do well, but that's because she wasn't a mainstream act at the time. Rabbit Heart was her first song to be picked up by radio, so because of that I tend to view it as her debut single, it was certainly her breakthrough single. Lungs debuted at number 2, it did well upon release. It's not like it underperformed, it was Michael Jackson who blocked her. The BRIT Awards hype is what propelled her to number 1. Everything did come together for her quite nicely in the UK, "You Got The Love" was a sleeper ht. It became huge after it was used in advertisements for Sky and Channel 4.
If she could perform on a big show over there she could probably break through. I think the fact Dog Days is on their itunes just after being on a trailer is a good sign as well as MTV video nominations. But compared to other British people who've had recent success in America (Taio Cruz and Jay Sean) she may be a bit too outside the mainstream