Tootie was introduced in the Oh Yeah! Cartoons episode "The Fairy Flu", in which she already had a crush on Timmy. Her appearance was redesigned in her Season 2 re-introduction "Boy Toy" to what it is today. Interestingly, in the comic The Big Surprise which was released in between these two episodes, Tootie's appearance is a cross between both her original and her redesign.
In her first appearance, Tootie was voiced by Amber Hood, from her season 2 re-introduction-onward, she is voiced by Grey DeLisle (who also voices Vicky, Veronica, Chad, etc.)
It was unknown if Tootie is her real name or nickname, but it is usually written everywhere in her room or on banners during her birthday, and in a deleted scene from Boy Toy, Timmy, Chester, and A.J. make fun of her name as well, so it is likely it's her real name.
Her name is possibly a homage to a character of the same name from the 1979-88 TV sitcom The Facts of Life. The Tootie in that show was also geeky, wore braces, and was the youngest of her group.
She usually appears at least once per season, except for Season 1 which had only six episodes, or Season 8 and Season 9 in which she hasn't. Her appearances became more frequent in Season 5, but Season 6, she barely appears. Tootie has made more appearances in Season 7 than any other, although most of them are just cameos. Her only appearances in Season 8 and Season 9 are live action. Lights Out is her last cartoon appearance to date.
Tootie is frequently a victim of improper animation. In many scenes her glasses are missing their temple arms, or her black tights will be missing. From Season 6 onward her glasses are drawn more simplistically round and change between purple and black color, depending on the episode.
Tootie may be aware of Timmy's crush on Trixie, as shown in You Doo, when she was playing with the Timmy doll, unintentionally causing the real Timmy to act rude to Trixie.
Tootie has kissed Timmy six times: Once in The Fairy Flu, a number of times at the end of Love Struck!, near the end of Kung Timmy!, Timmy kissed her near the end of Birthday Wish!, and in Dread N' Breakfast Timmy kissed Tootie again but refused to do so on the lips. Timmy and Tootie finally shared a very long kiss on the lips in "The Fairly Odd Movie", which resulted in Timmy instantly being considered a grown up by Da Rules and thus losing his fairies for a short time.
The Fairly Odd Movie also showed Timmy being forcibly kissed by Tootie when they were younger, and established that this kiss is the only one that Timmy could remember. According character bios on movie's press website, Tootie and Timmy's childhood kiss was done on a dare, but this is never elaborated upon in the movie itself.
Tootie appears more in Season 7 than any other season. However, along with the general increase in bizarre episode plots, Tootie's character was taken to extremes that many of her fans disagree with, including dressing up like Trixie to try to steal Timmy, saying she visits a psychologist over Timmy, and attempting to knock Timmy out with a paddle to give him CPR.
This also lead to even bigger extremes, such as the fact that there was nothing past Season 5 that stated her and Vicky were sisters, leading fans to think that the creators forgot that fact. Timmy's 2D House of Horror is the last episode where Vicky and Tootie interacted, and Mooooving Day is the last time they were seen on screen together. However, in Merry Wishmas, they were shown to still occupy the same house, although it moved right next to Timmy's house (erroneously in the spot Dinkleberg's occupied, for the sake of putting Vicky within Timmy's line of sight from his own house) when Vicky was seen collecting her Wish Coupon.
Tootie shares some noticeable similarities with Sam Manson from Butch Hartman's second Nicktoon, Danny Phantom. Among them, Tootie and Sam both have black hair and purple eyes, their outfits look similar, they're both voiced by Grey DeLisle, and both girls are in love with (and ultimately end up with) their respective show's protagonist.
Tootie's personality is somewhat similar to Sierra's from Total Drama World Tour or Clamantha from Fish Hooks. She also sounds very similar to Berry from Fosters Home for Imaginary Friends and Lizzie Devine from Kids Next Door, both also voiced by Grey DeLisle.
As of yet, it was never explained as to why and how Tootie developed her crush on Timmy in the series. In the Fairly Odd Movie, Tootie mentions that she has been in love with Timmy since 3rd grade.
In Schools Out!: The Musical, Tootie is seen with Trixie as they sing Adults Ruin Everything. This is the only time they appeared together in the series, with the exception of a brief scene in "Love Struck". Neither time do they interact. Tootie was also present at Trixie's costume party in "Take and Fake", dressed as Trixie, but it was never explained why and they do not appear together in person.
In the episode "You Doo", it is implied that Tootie dislikes Trixie. In most other episodes however, she seems oblivious to Timmy's crush on her.
In season 6 and season 7, Tootie's glasses are round, like her mother's.