My googling has been fruitless. It's going round and round in my head but just a few lyrics which may or may not be anything like the actual lyrics.
Clues: I suspect it's fairly recent, I listen to R6 a lot so most likely that's where I've heard it. It's a female voice, quite delicate and girlish.
It's poppy and upbeat as opposed to rock/indie/dance, and the lyrics go something like
We started a fire, something flame, let it burn, something all over again...