If she releases fun and happy music, she's childish and needs to grow up and should stop catering to the tweens. If she releases something that's a little more serious to her that's slow, then she's wrong for trying something different and shouldn't change because it's not the typical happy music she normally does.
So you don't like her fun songs because they're not mature enough, and you don't like her doing something more grown up because it doesn't fit her younger image. Make up your minds, or just don't pay attention to her at all.
Her sound of music doesn't have fit her "face," even if it does seem odd. She's might look 16 but she is in her twenties now and that's just a fact. Whether she writes her songs or not is irrelevant when we like others who don't write or only write occasionally. Writing doesn't give you the privilege to experiment or try new things, while others have to stay doing the same thing because they don't write.
I don't even care about her or like this song, but you are guys are so ridiculous with your complaints and judgmental POVs sometimes.