Betty Quinlan is Nick's female counterpart, as well as Jimmy's first love interest and one of his best friends. Jimmy frequently tries to get her attention with his inventions and flirts with her, and Betty flirts back to Jimmy, seemingly charmed by him, much to Cindy's jealously. Betty attends Jimmy's school, but does not take any classes with him or his friends and seems to be slightly older than them.
Betty is taller than the other girls in the franchise. She is very pretty, has brown hair, pink eyelids and a beauty mark on her cheek. She wears a pretty pink dress with white frills and turquoise Converse sneakers.
Betty's first appearance was in the episode Party at Neutron's, where she was one of the kids who attended Jimmy's party. She dances with Jimmy, and gives him a kiss on the cheek when she leaves his house.
Betty's second appearance was in Out Darn Spotlight, as the main protagonist. She was shown to be a talented actress, as she was given the role of Lady Macbeth in their school play "Macbeth in Space." Nick originally was supposed to play Macbeth, but Jimmy was forced to take over the role after Nick was injured. Naturally, Betty was Jimmy's motive for wanting to be in the play in the first place, and she seems to know this, and offers him kind encouragement. Towards the end of the episode, Betty kisses Jimmy on the lips, because they had not gotten to do so on stage and for saving the play and their lives.
Betty's third appearance was in the episode One of Us, where she was hypnotized by Grandma Tater's The Happy Show Show, along with many other Retroville residents. When Jimmy saw Betty as a zombie, he ran away.
Betty's fourth appearance was in Vanishing Act, where she is once again, the protagonist. Jimmy attempts to perform a magic show in order to impress her. However, as a result of Cindy's jealous actions, the magic show goes awry, and they end up stuck in another dimension. Jimmy and Betty continue to flirt, which angers Cindy to the point of furiously attacking them over it and blaming the whole thing on both Betty and Jimmy (which Jimmy calls her out on). Betty eventually gets fed up with Cindy's nasty attitude towards her and calmly pulls her aside to explain to her that she knows about Cindy's crush on Jimmy—Betty admits to Cindy that she knows that Jimmy has a crush on her [Betty] and says that she's flattered by it, but ultimately, she doesn't like/care about Jimmy as anything more than just a friend. Betty tells Cindy stay out of her face and that Jimmy's all hers—this proves that while Betty and Jimmy are best friends, she is flattered and appreciates Jimmy's affections toward her, but she knows he belongs with Cindy and is fully supportive of their relationship, but it's hard to show it because Cindy is always mean to her.
- Betty and Cindy's relationship is similar to the relationship between Betty and Veronica from the Archie franchise. However, Betty looks more like Veronica and Cindy looks more like Betty.
- During the cancelled season four, there would have been an episode called "Three's a Crowd", where Cindy, Libby and Betty would've gotten trapped in Jimmy's lab and have to work together to get out. In this episode, Cindy would've finally come clean about her resentment towards Betty, they would've opened up to each other and at the end, the girls would've become friends.
- Betty is implied to be slightly older than Jimmy and his friends, since she's not in any classes with them and is taller and even looks a little older.
- It is revealed in The League of Villains that Jimmy still likes her, since he was shown to still have many pictures of her in a drawer in his lab and one in his captain's log, which Cindy made him get rid of upon discovering them.
- Sometimes, it is hinted that Cindy might be secretly fond of Betty since was smiling and giggling at the picture of Betty in The League of Villains.
- Besides the episodes in which she is a main character, she is also a background character in the show.
- Nick and Betty being cast as Macbeth and Lady Macbeth could've been a reference to the fact that Jimmy and Cindy both have had crushes on them. Nick and Betty enjoying the roles could also hint romantic chemistry between them.
- "TIME OUT!! Cindy, we need to have a little chat... Look, I know all about the whole 'you and Neutron' thing...Just stay out of my face. He's all yours." -Vanishing Act
- (In Jimmy's daydream) "Oh, James..." -Operation: Rescue Jet Fusion
- "Kiss me, my king of the stars!" -Out, Darn Spotlight
- "Great party, Neutron!" -Party at Neutron's
- "Sure, Jimmy! I love magic!" -Vanishing Act