Jeanette was born in Australia and can best be described as the "absent-minded professor" of the group. Gifted with extraordinary intelligence, she often is so caught up in contemplating the universe that she forgets the simple matters of life, such as not tripping over her own feet. She is actually more like Theodore than Simon when it comes to her personality, as they are both sweet, timid, and shy, but her interests and talents are closer to Simon's. Jeanette is nearsighted. She is also incredibly clumsy. Jeanette gets along well with Simon of The Chipmunks, however, they are very shy of their relationship.
Jeanette's age in regards to her sisters is never stated in the films. Despite not having a stated last name either, it is presumed to be Seville because of The Chipettes being taken in by Dave at the end of the second film. However, this naming would be controversial, as it would make her Simon's adoptive sister in addition to his love interest.
Though her CGI version retains many of the traits she had in the 80s series, there are some notable differences. She has an insecure personality, regularly saying "I'm not good with things like this." However, she eventually learned to be brave and take more risks, though still being cautious. She is also slightly more outspoken, sometimes surprising even her sisters. Though this may be seen in the third movie, she is not shown to be very clumsy at all; when dancing and performing, she can actually keep up well with her sisters and The Chipmunks, never faltering or stumbling.
Jeanette's age in regards to her sisters hasn't been stated in the series so far though she retains the last name Miller as stated in Jeanette's Secret Garden.
Jeanette is initially shown to be very gullible (as in Jeanette Enchanted where she believed she could fly when Alvin blew cayenne pepper in her face) in her past, but has worked (mostly) past it. She retains her shy, insecure personality, though less pronounced as she works past it with the help of Alvin (My Sister The Weirdo). She isn’t as clumsy as she was in the 80s series. She is interested in astronomy (in galaxies, to be exact) as Jeanette and Simon named their baby Galaxina (Baby Mama Drama) but has shown her surprising abilities as a cat whisperer (Good Luck Mr. Whiskers). Additionally she is into chemistry as she is seen working on a partner project with Simon in Lice-enced to Teach. Not only that, she seems to be more eco-conscious in comparison to previous incarnations (The Tree House), where she nonviolently protests against their tree-poisoning neighbor, Mr. Crabble, by living in the tree that would become The Chipettes' tree house, refusing to let it get cut down by him. She also seems to be more mature compared to her previous incarnations. She can also play the guitar skillfully (The Tree House, Wax Dave).
In the Alvin and the Chipmunks series, she is brunette with her hair pulled up in a messy bun and (dark in the first 5 seasons and then teal in seasons 6-8) colored eyes. Her signature color is purple. She wears a cornflower color turtleneck sweater with baggy sleeves, a purple skirt, and blue slip ons. She has black glasses in the first season of the series and in Alvin and the Chipmunks Meet the Wolfman while having pink glasses in the second to the final season as well as the specials.
In the CGI films, Jeanette has violet eyes and purple glasses. She also has brown fur. In Alvin and the Chipmunks: The Squeakquel, she wears a blue denim jacket with a light purple shirt, a blue/purple skirt, and a silver sparkle dress. In Alvin and the Chipmunks: Chipwrecked, she wears a purple and white striped shirt (with her sleeves rolled up) with a blue white-starred skirt held by a purple belt, a purple-sparkle dress, and purple-flowered garments. In Alvin and the Chipmunks: The Road Chip, she wears a purple and white striped shirt and a skirt with white, pink, and purple rectangles between blue vertical and horizontal stripes topped with a black belt.
In ALVINNN!!! and The Chipmunks, she is a brunette with her hair pulled up in a bun (with a few loose hairs on the sides in front of her ears) with a purple band or occasionally a purple clothespin. She has violet eyes with violet eye shadow and lilac glasses. She wears a collared flannel shirt of various shades of purple (the top button unbuttoned) with a zippered purple hoodie with lilac fleece inside, dark blue jeans, and plum purple slip-on loafer shoes.
Jeanette isn't brave enough to stand up to Brittany (but she tried to stop Brittany's attempt at robbing Galaxina in Baby Mama Drama). Brittany pushes Jeanette around a lot and takes advantage of her, but deep down they love each other very much and are very loyal to each other. Brittany gets very defensive of Jeanette when someone else is mean to her, in most situations. Even when Brittany is rude to Jeanette, she is extremely loyal despite her behavior towards her, saying "You're my sister, Brittany."
Eleanor always stands up to Brittany when she tries to push Jeanette around, and always defends her when anyone says something negative. For example, refusing to help Brittany join a group that called Jeanette a nerd.
Jeanette and Alvin are friends. It's not uncommon for Alvin to stick up for Jeanette if someone is spreading lies or taking advantage of her, but there are still a few times Alvin uses her such as in My Fair Chipette. He has also shown moments where he becomes defensive of Jeanette as in Sisters when Brittany is ignoring her. He played Jeanette's boyfriend in Chip Tracy, but they are actors in this episode. When Jeanette lands the helicopter in the school on the day of the Music Mania, Alvin and Jeanette high-five each other. In My Sister The Weirdo, Alvin helps Jeanette get over her shyness at her request.
Simon and Jeanette have a very strong relationship. During the series it is a relationship that can be described as best friends who have secret crushes with one another. Simon is always looking out for Jeanette and stands up for her. Simon seems very protective of Jeanette, and the two of them spend a lot a time together. In My Sister The Weirdo, it is shown that Simon can be jealous if others help her instead of him. In Secret Admirer it shown that Simon likes her, but he's just too embarrassed to admit it.