What is your source for this number?
Also, considering the amount of people that contributed to this song, a low margin is not surprising. There are at least 4 different producers who no doubt also had a hand in writing. There are 11 officially credited songwriters, not to mention the producers themselves who often get writing credits as well. Not to mention anyone who may be uncredited but have asked for some kind of royalty or payment for their contribution.
Just because she sung the hook and contributed to the songwriting process doesn't automatically mean she is going to get the biggest cut.

If anyone gets a big cut it would be the producers. Then you have to factor in the label, publishing, management, distribution, etc.