it's easy to say "well, she's doing it on purpose. she's singing in microtones". that's rather unlikely, in pop music of this nature. the truth is likely more along the lines of that she's truly tone deaf, and she's not able to hear the wrong notes (or correct notes) properly. it's actually relatively common in pop singers, but somebody usually gets in the way and fixes it - in the past by yelling at the singer to practice, and nowadays, more often than not, by simply using autotune.
despite that, the dissonance is sort of compelling - or would be if it wasn't so repetitive. but, the repetition is a genre marker. the industry refers to this monotony with the term "hook".
there's only one singer that i'm aware of that's been able to convert being tone deaf into an actual asset, and it's the original singer from alice in chains, layne staley. he could yell pretty well, but he couldn't hit a note if his life depended on it. but, the guitarist in the band really played off of this to create all these harmonies that are just completely outside of western music theory, and the whole thing was wrapped up in a thematic package that really took it to the next level. you can hear the difference in listening to older songs performed by their new singer. the new singer is not tone deaf - he actually hits the right notes. and, the songs lose this kind of intangible (not really - i just explained it) as a consequence of it. you expect the singer to be off by that quarter tone, and are offset when the correct note is produced.
success in pop music is driven by factors that are often very far removed from musical talent, creativity or ability. i'm not suggesting her career is over, because it does not seem to have been dependent on her actual singing ability in the first place. but, it's not the first time that it's been blatantly clear that she's either tone deaf or singing in microtones, and it's really only the former that is at all likely.
a few more releases like this, though, where the most memorable part of the song is how badly it is sung, and people are going to start noticing in larger numbers.