Nicki was the ex-girlfriend of Jake Jagielski and the mother of his daughter, Jenny. After giving birth to Jenny, however, she left Tree Hill, leaving her daughter to be raised by Jake and his parents for the first eight months of her life. Upon returning to town, Nicki attempts to become part of Jenny's life, but Jake refuses to be involved with her. This causes major problems and she becomes an antagonist to Jake and Peyton Sawyer.
Nicki was first introduced in a bar where she met Lucas Scott and had a one night stand with him shortly after he broke up with Peyton and Brooke. Nicki shows up at Jake's house and announces that she wants to be a part of Jenny's life. Nicki bids on Jake at the "Boy-Toy" auction, winning against Peyton. Jake is angry that he had to raise Jenny alone and Nicki was no where to be found for the past 8 months. Nicki says that she felt horrible about it, but she wasn't sure if she would be a good mom and she got scared because all her friends were heading off to college. She also tried get back together with Jake. Nicki tells Jake that she will be a part of Jenny's life, with him or without him. After not being invited to the party that Haley was throwing at Nathan's apartment, Brooke went to a bar and met Nicki. They showed up at Nathan's apartment and Peyton, Nicki and Brooke were constantly fighting with each other. Nicki started a fight with Peyton and destroyed Nathan's apartment which caused Nathan to be arrested. Nicki kidnapped Jenny from Peyton and Brooke when they were in the shopping centre, Jake got Jenny back and fled Tree Hill with Jenny. She tried to use Brooke to find out where he was but was fooled into going to Seattle while he was actually in Savannah.
She returned in season two, saying she had earned custody of Jenny through a trial which Jake did not attend because he was in hiding. When Jake refused to give Jenny to her and turned himself in to the police because there was a warrant out for his arrest, she still managed to locate her and take her away. Jake then chased after her.
In the third season, Jake reveals that he and Nicki were both living in Savannah and will continue sharing custody of Jenny until the next trial.