Betty Quinlan is Jimmy's first love interest and a supporting character in the series.
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 proceeds to call her out on).
Betty eventually gets fed up with Cindy's nasty attitude towards her and calmly pulls her aside to talk to her. Betty reveals that she knows Jimmy has a crush on her and that Cindy has a crush on Jimmy, and explains that while she's flattered that Jimmy likes her, she doesn't like him as anything more than just a friend. Betty tells Cindy to stay out of her face and that Jimmy is all hers, indicating that Betty also feels that Jimmy and Cindy would make a better match for each other than Betty would for Jimmy.
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, a belt, and a pair of turquoise and white Converse sneakers.
Betty's shown to be nice towards Jimmy, who frequently tries to get Betty's attention with his inventions and flirts with her. The latter of which she reciprocates, seemingly charmed by him, much to Cindy's jealously. Betty, unknowingly or not, often prompts Jimmy into doing things he wouldn't normally do, like mess with Nick's rehearsal for MacBeth in Space, which involved a scene in which Nick would kiss Betty.
Despite her kindness towards Jimmy, Betty acknowledges that Jimmy and Cindy have feelings with each other. She revealed this to Cindy and told her to "Just relax and keep out of [her] face. He's all yours".
- "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
- 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 she was smiling and giggling at the picture of Betty in The League of Villains.
- Nick and Betty being cast as Macbeth and Lady Macbeth in Out Darn Spotlight could've been a reference to the fact that Jimmy and Cindy both have had crushes on them.
- Besides her four official appearances, Betty also made numerous cameo appearances in Krunch Time, Make Room for Daddy-O, Return of the Nanobots, Send in the Clones, The Great Egg Heist, Billion Dollar Boy, Attack of the Twonkies, My Big Fat Wedding Spy, Jimmy Timmy Power Hour 2: When Nerds Collide!, and Jimmy Timmy Power Hour 3: The Jerkinators! as a background character and without any lines. In Operation: Rescue Jet Fusion, she appeared Jimmy's daydream sequence as his leading lady where she said one line, "Oh, James" but does not appear in person.