The Bone Shard War - Andrea Stewart

From the author of The Bone Shard Daughter comes the final book in the Drowning Empire series, as the fate of Lin Sukai—and her family's dynasty—lay in her hands in this action-packed, magic-laced epic fantasy.
Lin Sukai has won her first victory as Emperor, but the future of the Phoenix Empire hangs in the balance – and Lin is dangerously short of allies. 
As her own governors plot treason, the Shardless Few renew hostilities. Worse still, Lin discovers her old nemesis Nisong has joined forces with the rogue Alanga, Ragan. Both seek her death.  
Yet hopes lies in history. Legend tells of seven mythic swords, forged in centuries past. If Lin can find them before her enemies, she may yet be able to turn the tide.  

If she fails, the Sukai dynasty – and the entire empire – will fall.