Is Bella really in "The Host," or is it just a rumor?
“The Host” is the first adult novel by Stephenie Meyer. It deals with the theme of relationships when two beings inhabit the same physical body. The plot involves an alien species called Souls. They invade human bodies and take over the personalities of the person. Melanie Stryder, is the protagonist and one of the few human holdouts. She has been captured by the aliens and is implanted with a Soul named Wanderer, who is something of a legend among her own kind because of the many hosts and planets she has experienced. Melanie won’t give control to Wanderer . Wanderer is overcome by Melanie's memories and feelings. The book contains some science-fiction, some romance and some mystery. Bella is not in this novel.
Bella is not a part of that. That is a completely different world and although it is a part of her work but I don't think she would include someone else from her previous stories into a new book set in a different world.
Bella most certainly did not make an appearance. The host is a completely different world from Twilight and it has a dystopia like feeling towards it. Instead of vampires running around it's more like alien parasites trying to live vicariously though humans. Stephanie Meyer once commented how it was nice to work on something that was completely different from the Twilight series. So I doubt she would add characters from a one of pieces of work that just doesn't fit into the story.