Charli is such an amazing and talented artist, and her debut was full of GREAT pop songs filled with hooks. To the answer the OP though, she's paid dust because her name isn't really out there. I mean sure she wrote I Love It but no one ever saw her perform it with Icona Pop on TV or even knew she was involved so Fancy is her introduction to the GP and people will look her up and hopefully it'll help her garner a bigger fanbase.
Even if she doesn't become super successful the girl knows how to write fantastic hooks so the pop industry will definitely want her to write some things for tons of other artists, and if those future songs are hits it'll allow her to be able to make the music she wants and she won't have to worry about money. Remember success can sometimes cripple an artist because of how record labels want them to rehash old stuff and follow trends, so maybe she's better off being the "hook-girl".
