When Bella gets bit by James in Twilight, she isn't dying, all that is happening is James's vampire venom is getting into her bloodstream which is starting the painful process of a human to vampire transformation.
Chat with our AI personalities
Bella isn't really sick she is just giving a baby. When you have a baby you are usually sick your entire pregnancy.
Bella is dying from loss of blood after James, the vampire, bit her and caused severe injuries. She is also in danger of turning into a vampire if she doesn't receive immediate medical attention.