A Wasteland of My God's Own Making. The Song of the Shattered Sands, #1.4

Djaga Akoyo left the grasslands of her homeland long ago and rose to prominence in Sharakhai's fighting pits as the famed Lion of Kundhun. What Djaga revealed to no one, however, is the terrible secret that drove her to leave Kundhun in the first place. That secret is brought back to the fore when her sister tribeswoman, Afua, comes to Sharakhai unannounced and threatens to reveal her shameful past, a thing that would upend the life Djaga has worked so hard to build for herself.
Djaga and Afua's pasts are linked. Afua tells her that with one final bout in the killing pits, both their demons will be excised. But Djaga has more to worry about than Afua's demons, or even her own. She has Nadín as well, a woman she hopes to share a life with once she's left the pits for good. But how can she start a new life with Nadín when the terrible acts she committed in her homeland still haunt her?Djaga must decide once and for all whether she'll face them, but in doing so she may lose the one she loves.