Isabelle is very clumsy and absentminded and dislikes confrontation. Despite this, She is respectful of others and is very friendly. Being open-minded and friendly, she is very keen to make the town a better place to live, by encouraging the player to do tasks and Public Works Projects throughout the town. Like many other secretaries, she can be hard on herself when she is side-tracked. Isabelle has shown sides of gratitude and affection to the player, especially on Valentine's Day and is even hinted on having a crush on the player regardless of gender.
In New Leaf
Isabelle is a nearsighted bright yellow dog who resembles a Shih Tzu, which her Japanese name, Shizue, is a play on. Her head is also shaped like a bag of bells, hence the English name. She has a happy appearance with rosy cheeks and with a white fur patch on her tail and around her mouth. She wears a green checkered vest with a white top and a red ribbon underneath with a navy blue skirt. During fall and winter, she wears a yellow cardigan instead of a vest. Her hair is tied up with a red ribbon with bells attached which actually jingle as she walks.
She wears different styled clothes on special events that are held around the town; for example, she will wear a flowery shirt during the Fireworks Show and a Santa-style shirt on Toy Day.
In Animal Crossing: Happy Home Designer
Isabelle is an optional character who can move into the village where the player makes houses. She heads development of the town coming to you to help make certain places like a School, Cafe, Hospital, and Store.
In Monster Hunter 4 Ultimate
Capcom revealed outfits based on Isabelle and Mr. Resetti via its Unity blog, and confirmed that Felines' meow sound will be altered accordingly when they are equipped.
In Super Smash Bros. Wii U/3DS
Isabelle was confirmed to be an assist trophy character in Super Smash Bros. Wii U/3DS, on the 4th of March, 2014 in the Wii U version (although she is also present in the 3DS version). She was shown again in the Super Smash Bros in the Nintendo Direct on the 8th of April. Later on, she was confirmed that she will help the fighter who summoned her by throwing fruit towards them that can be 'eaten', lowering their percentage but fighters cannot interact with her. An Isabelle Suit for the Mii Gunner was included as part of Smash Bundle #2 as well.
In Taiko no Tatsujin: Atsumete Tomodachi Daisakusen!
In Taiko no Tatsujin: Atsumete Tomodachi Daisakusen!, Isabelle appears alongside with Tom Nook and Resetti as unlockable content via amiibo cards or figures being activated. Activating any Animal Crossing amiibo product may unlock other features from in-game features to soundtrack from Animal Crossing: New Leaf.
In Mario Kart 8
Isabelle has been confirmed as a DLC character, along with the Villager, for Mario Kart 8, and has been available since April 23rd, 2015.
Advice for living in Town
Asking Isabelle for advice for living in the town is a sub-quest the player can do. She will repeat advice several times even if finished. Apart from listening to her advice, the player is asked to buy a shovel, collect one seashell and catch either three bugs or fish and eventually receives a basket of non-native fruit and a watering can. She does not always give this quest. If the player can't find a shovel and go talks with Isabelle, she will give the player a shovel.
Depending on what the player's native fruit is, Isabelle will give the player a certain non-native fruit:
"Is there something I can help you with today?"
— Isabelle, offering the player assistance.
"Oh, is that all? Well, we'll just.. WAIT, WHAT?! "
— Isabelle, when asked to demolish the player's house.
"OK! The town will be... WAIT, WHAT?! "
— Isabelle, when asked to delete the town.
"I must say, I'm a fan of K.K. Slider myself..."
— Isabelle at the introduction spotlight, after Club LOL has been built.
Isabelle has her very own Twitter account, sending news about "Animal Crossing: New Leaf" every once in a while as of May 6, 2013: @animalcrossing
Isabelle shares her birthday with Digby, since they're twins.
Her English name, Isabelle, possibly comes from the resemblance of her head to a bag of Bells (Isabelle = 'is a Bell'). She also wears a red ribbon with bells that jingle when she walks.
Her Japanese name, Shizue (しずえ,Shizue?) may be interpreted as "quiet branch," perhaps referring to the tranquility of an Animal Crossing town. It can also be derived from her dog breed name "Shih Tzu".
Her Spanish name is Canela (Cinnamon), a symbol of wisdom and good health. "Can" (Can-ela) is also another word for dog in Spain, and it is used in the Spanish version of the game with her brother's name (Candrés) as a pun.
Her French name is Marie, a pun on the word Mairie (Town Hall) or Maire (Mayor).
Her Italian name is Fuffi, a pun on the fact that she is a dog.
One of the only ways to get Isabelle's coffee preference is through her twin brother Digby.
Isabelle changes her clothes starting on the second-half of October and ending at the 25th of February.
She is seen to sleep in Town Hall, and when the player goes up to the front of the counter, she wakes up with a surprised look on her, and then acts embarrassed.
Isabelle only has one tooth.
Isabelle mentions having a band upon completion of the concert hall in Happy Home Designer.
Isabelle has the voice of a peppyvillager, but her shown personality indicates that she is normal.
Sometimes if the player talks to her while visiting another town, she'll tell the player that she has many sisters who look exactly as her, that work as secretaries in other towns, and are all named, of course, "Isabelle".
When first announced, during the New Leaf developer commentary, Isabelle was not given a name, but was referred to as simply Secretary (ひしょ,Hisho?), then named in the June 2012 Nintendo Direct as Shizue. Her name was changed in February 14th, 2013 at the Nintendo Direct to Isabelle, to localize her in English.
Sometimes if the player talks to her while she's visiting the campground in the Welcome amiibo update, she'll reveal she's actually nearsighted, hence why she wears glasses with her casual outfit.