Teddy R. Duncan  is the older sister of Charlie. She creates a video diary for her little sister to ensure that she survives their "special" family. She is the second oldest out of the 4, now 5 Duncan kids.
Teddy is a kind, intelligent, creative, responsible 16 year old girl who cares about her family and friends. Teddy loves to go shopping, hang out with her best friend, Ivy, and go to the movies. It is suggested that her favorite colors are blue and purple. Teddy gets excellent grades and excels in English, math and science ("Teddy's Little Helper"). She also likes music ("Take Mel Out to the Ball Game"). It is also suggested that she enjoys acting as she auditions for the role of Beauty in her school production of Beauty and the Beast, in which she was the Beast, and she was in her school's fourth grade production of The Sound Of Music ("Sleepless in Denver"). It is unknown which part she plays but Bob finds a flier to her production ("Charlie in Charge"). Based on her appearance and personality, she probably got the part of Liesel or Maria. Sometimes her best friend Ivy calls her "T".
Teddy can get easily distracted, especially if it comes to her high school crush, Spencer. However, Teddy is sometimes shown to be jealous or angry. She got angry at PJ for bringing home the wrong baby from the park ("Baby Come Back"). Teddy gets jealous when her best friend Ivy becomes textmates with her mother. She sometimes hides secrets from her parents in a few episodes ("The Curious Case of Mr. Dabney"). Teddy also is easily embarrassed, especially by her family members. She blushes when Spencer's rich parents see her family members acting ridiculously on the local news. After admitting to be related to them, she actually burps out loud twice and can't deny who she is and confesses to frequently sweating, farting and burping ("Charlie Goes Viral"). Teddy can also be extremely sensitive about her grades. She gets upset and even a little mad when she gets her first B ("Teddy's Little Helper"), even though Bs aren't that bad. She goes as far as even using Charlie just to please her teacher and get an A. In "Teddy's Bear", she angrily snaps the point of her teacher's pencil when he refuses to change her grade and ends up getting detention. She also gets mad at her ex-boyfriend Derek when he's not upset that she broke up with him, as she was expecting him to make a big deal out of it and beg her not to break up with him. Her catchphrase is "That's so unfair" based on people in her life being unfair.
When she turned two, she wanted a Howdy Puppy. She never got one, and still is upset about it ("Charlie is 2!").
Teddy has a study date with her crush Spencer. But because of the annoyance of their family, their study date is always interrupted, which irritates Teddy. Also, when Bob slips and falls down the stairs, Teddy has to take care of Charlie, while PJ drives Bob to the hospital and they both try to avoid Amy ("Study Date").
Teddy becomes jealous of her best friend Ivy when she becomes textmates with Teddy's mom, Amy Duncan ("The Curious Case of Mr. Dabney").
A dance is approaching at school. Teddy asks Spencer out for the big night and Ivy asks out Emmett. Teddy tries to get her first kiss from Spencer, but Emmett, who also likes Teddy, distracts Spencer from Teddy by hip-hop dancing with him. Eventually, however, she is able to kiss him in Emmett's grandfather's car ("Dance Off").
Teddy lies to her mom that she liked her top and that Teddy wanted to be with her more then Ivy. When Teddy butt-dials Amy and she picks up, Teddy didn't hear anyone so she put the phone down without turning it off. Mom hears everything when her and Ivy were talking about how uncool Teddy's mom really is. The reason why Teddy pretended that Mom was cool was because that she wanted to see Dusk,( a parody of Twilight) although the movie was premiering on Thursday at midnight and Amy did not let Teddy stay up late on school nights ("Butt Dialing Duncans").
Teddy has long, blond hair that she wears in loose waves most of the time. She is tall. Most of the time she can be seen wearing her hair down. She can mostly be seen wearing boots, and she asks PJ for them for her sixteenth birthday ("Driving Mrs. Dabney"). Teddy usually wears jeans paired with a loose blouse or sequined tee and a long sweater. She has a slightly boho fashion sense.
Teddy loves her mother. They have a strong bond. However, in some episodes Teddy lies and tricks her mother. She wants to see a midnight movie with Ivy, and to trick her mother into letting her go, Teddy hangs out with her for the day and tells her she's cool ("Butt Dialing Duncans"). Teddy confesses to her mother that she wishes they wouldn't have had another baby ("Pushing Buttons"). Teddy goes to her mother for advice about boys ("Snow Show, Part One").
Teddy and PJ have a common brother-sister relationship. They fight but they are always there for each other.
Teddy does not like that her dad is a pest control specialist. She says "he kills bugs for a living" ("Study Date"). However, she loves her father very much. She wouldn't trick him into buying her a car like she had planned because she loves him too much. ("Termite Queen")
Teddy has said she was kidding when she said she was never interested in him, so that means she and Gabe have a strong bond. ("Study Date"). Teddy helped Gabe by pretending to be his mom, even though she failed. She did teach Charlie that the opposite of good was Gabe, but she still shows love for her younger brother. The same is for Gabe when he and PJ make a rap for her 16th birthday, and before attempted to buy her shoes.
Teddy loves her little sister. Teddy makes a video diary for her, because she figures she won't be around when Charlie is older. Teddy often takes care of Charlie. Charlie loves her back
Teddy once has a crush on Spencer. In Study Date, It seems Spencer likes Teddy back. They soon start dating. But this relationship ends when Spencer is caught cheating on Teddy at work with Teddy's soon to be friend Skylar. Soon after that they kiss, but they decide to just stay friends, but they seem to hate each other, calling each other a clump-nugget ("Battle of the Bands"). After a while Spencer and Teddy get back together and are dating again.
Teddy and Ivy have been best friends for a long time. Their mothers are also friends. Teddy sometimes doesn't trust Ivy's opinion.
When Emmett says their relationship with Teddy ended when he was dating Nina, Teddy responds that their "relationship" was all in his head ("Pushing Buttons").
Emmett gets Teddy a job at Super Adventure Land as a princess.Emmett also works there as a frog and Teddy and Emmett have to do a show together about The Frog Prince.
When Teddy has to kiss Emmett in a show at Super Adventure Land for her job, Teddy invites Emmett over so they can practice and see if they will feel anything between them. Emmett gets scared that if they don't feel anything, then their relationship won't have a chance after Teddy tries to be embarassing and insane, so he leaves and quits his job ("Return to Super Adventure Land").
- Amy says she picked the name Teddy because she liked the name, implying Teddy is her legal first name ("Pushing Buttons"). However, in Sun Show Part 1, Teddy tells Kai that she got her name because her parents were expecting a boy.