The Harvest. The Bone Gardeners Trilogy, #3

The continental ritual begins at midnight. In twelve hours, the immortal council will drain the life force of millions to achieve godhood - unless Kira Blackthorne can infiltrate their stronghold using the most dangerous technique in the bone gardener's arsenal: death itself. Transformed into a guardian spirit after stopping the council's network, Kira must now confront their ultimate plan - a ceremony that would make traditional mortality impossible across entire territories.
But the resistance she leads faces an enemy that has evolved beyond their projections: the Purist Alliance, enhanced humans who reject both cosmic partnership and natural death in favor of unlimited power without ethical constraints. As multidimensional entities take interest in humanity's transformation and communities fracture between those choosing enhancement and those defending mortality, Kira faces an impossible choice.
To preserve the right to die, she must coordinate transcendent capabilities that rival her enemies. To defend individual choice, she must unite populations whose fundamental beliefs about consciousness and community have become incompatible.