In the second book, new moon, Bella is found in the forest by Laurent one of the nomad vampiers. Laurent was associated with James before his death. Jacob then finds laurent and Bella in the forest, and saves Bella from the bloodthirsty vampire.
Chat with our AI personalities
when they are in the forest
Because he finds it interesting that he can't read her thoughts
So no one finds out where she and Jasper are going except for Bella because she is the only one who's thoughts cannot be read by Aro.
If you really want me to ruin it, in the last book, when she';s pregnant it's clear the half vampire half human baby will kill Bella, so Edward bites her and turns her into a vampire to save her life.
That's in New Moon when Bella finds out she can hear Edward's voice when doing something risky or dangerous. They went to go see Dead End