Well, perhaps in the fanfiction, Bella's transformation into a banshee is related to her love for Edward. Her intense emotions somehow trigger the banshee side of her. As a banshee, she could use her wail to warn the vampires of approaching threats from other supernatural beings. The story could then revolve around how she uses her new abilities to protect the ones she loves and also how the vampire community reacts to this new form of her.
One possible plot could be that Bella discovers her new banshee powers after some strange and traumatic event. Maybe she starts having premonitions not just about danger to herself like in the original Twilight series, but about disasters that will befall the entire town. This could put her in a position where she has to figure out how to control these powers and also how to convince others, like the Cullens, that she's not going crazy.
Chapter 185, "We Are the Real Team", is the clearest early answer because it turns Su Yinwan's situation into a concrete plot event. Early on, He was so anxious that he immediately picked up the megaphone.. By the end, The next, she'd complain that the ground was too slippery to walk on..
Chapter 356, "I announce, Lili is the best of the night!", is the clearest early answer because it turns Lili's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Seeing such a bustling scene, Su Yinwan who had just alighted from...
Chapter 254, "Madwoman! She is definitely a madwoman!", is the clearest early answer because it turns Jiang Yan's situation into a concrete plot event. Early on, Just when everyone thought that Jiang Yan wouldn't last long and....
Chapter 304, "Shh, Let's Not Disturb Big Sister", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. It opens with But his cries and screams didn't elicit the slightest sympathy from...
Chapter 347, ""I Want to be the Eagle in the Wilderness", is the clearest early answer because it turns Zhang Cheng's situation into a concrete plot event. A useful checkpoint is the way the scene starts with On the way there, Jiang Li had already learned quite a bit about the...
Chapter 438, "The Upper Stream is Mine, The Lower Stream is Yours", is the clearest early answer because it turns Sister Li's situation into a concrete plot event. Early on, I'm sorry," Shang Shuyue squeezed out three words through clenched....
Chapter 85, "They must have been bought off by Jiang Li!", is the clearest early answer because it turns Chixia Village's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Facing everyone's skepticism and curiosity, Jiang Li explained...
Chapter 369, "Who Makes Him the Omnipotent Male Lead?", is the clearest early answer because it turns Lin Manru's situation into a concrete plot event. Early on, But..." Lin Manru's tone shifted again, "Our studio has become....
Chapter 381, "You are Liu Suqing's Daughter", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. Early on, Yu Tiantian was even more baffled now.. By the end, If I hadn't carelessly handed you to someone else, you wouldn't have....
Chapter 279, "The Sudden Blaze", is the clearest early answer because it turns Wen Jiaojiao's situation into a concrete plot event. It opens with After getting a good scolding, Jiang Yan resigned himself to lying...