Sally Jackson was laying down on a hospital bed, dying. She knew she was dying but she wasn't afraid for her but her unborn daughter.
She prayed to anyone who was listening to spare her daughter.
And her last wish was granted by the Fates.

They transferred Sally's unborn daughter to the closest living relative, which was a woman named Isabella Cullen nee Swan.
Now Bella was pregnant also but she was pregnant with a half-vampire ,or "cold one", baby.
When the Fates transferred Persephone to Bella, Renesmee has now some godly blood but like a legacy percentage now and Percy has some vampire genes now too.

Character information

Edward Cullen
Bella Cullen nee Swan
Renesmee Cullen
Persephone Cullen