Binti has left her village, left the planet Earth, and is on her way to study math at the galaxy's most prestigious university. When the ship is attacked by the fearsome alien race called the Meduse, she turns to mathematics and the almost mystical powers it gives her:
(quoted from Binti)
And so I had become a master harmonizer by the age of twelve. I could communicate with spirit flow and convince them to become one current. I was born with my mother's gift of mathematical sight. My mother used it to protect the family and now I was going to grow that skill at the best university in the galaxy...if I survived. "Binti Ekeopara Zuzu Dambu Kaipka of Namib, that is my name", I said again.
My mind cleared as the equations flew through it, opening it wider, growing progressively more complex and satisfying. VE+F=2, a^2+b^2=c^2, I thought.

Harmonizers are peace makers, and the plot of the book concerns Binti's role in making peace between the Meduse and the university professors.
Although math is mentioned frequently, the quote above (featuring the equation satisfied by the edge lengths in a right triangle and the Euler characteristic for a connected plane graph) is the only one with any mathematical detail. Otherwise, there are vague references to blue fractals and thinking about numbers and how these control "currents".
The book never really explains what being a harmonizer has to do with math or how "treeing" (whatever that may be) allow her to do the things she does. But, it does state repeatedly that it is her mathematical ability that both endows her with the powers of a master harmonizer and made her the first of her people, the Himba, to be admitted to Oomza University.
This book reminds me very much of the story What it Means When A Man Falls from the Sky by Nigerian author Lesley Nneka Arimah. Both deal with cultural conflict and have primary protagonists who are young African women with innate mathematical abilities that they apply to problems involving emotions. Perhaps that is not a coincidence as Okorafor is an American born to Nigerian parents. (She teaches creative writing at the University of Buffalo.)
Thanks to Evelyn Lamb for suggesting that I add this book and the others in the Binti trilogy to my database. 