Who is Nikki Howard from Airhead #2: Being Nikki and what is their importance?

Nikki Howard is the supermodel whose body Em now occupies. Throughout the first novel in this series, as well as for most of "Being Nikki," Em believes that Nikki is dead, and discovers a lot about her personality simply by gauging the reactions of those around her. Apparently, Nikki was spoiled and self-centered, and had declared herself an emancipated minor at the age of sixteen, though her brother Steven shows Em that they actually had a pleasant mother and childhood, just not a very glamorous one. Nikki has lied to everyone and told them that she comes from New York, when she in fact comes from a small town. She has done everything she can to put her past behind her. When she heard Mr. Stark discussing confidential secrets about his new video game, however, her scheming side took over and she tried to blackmail him. Rather than fall to her demands, though, Stark simply had her brain replaced by Em's. The doctor who performed the surgery, Dr. Fong, realized how unethical his work was and placed Nikki's brain into another body. In a frumpier form, Nikki is furious when she meets Em and wants her old body and her old life back.