From Nookipedia, the Animal Crossing wiki
Labelle (ケイト, Keito) (also known as Label by her sisters) is the store clerk for GracieGrace in Animal Crossing: City Folk and a clerk for the Able Sisters in Animal Crossing: New Leaf. Her name is similar to "label", a nod to how she used to work at a designer store; "Label" also rhymes with the names of the other two Able Sisters.
Labelle is a hedgehog with a black dress and "Gracie shirt" style neck tie. In New Leaf her tie pattern has been changed to an orange gingham pattern.
She is in charge of GracieGrace, as Gracie herself appears uninterested in maintaining her own store, due to her celebrity status. She is apparently a long-lost third Able sister, even though the other two have not talked about there being other family besides their mother and father who died when Mabel and Sable were very young, and despite any evidence of this sister never existing until now. Sometimes, if the player stays at the Able Sisters after closing, they can talk to Sable, and she remark how the player hasn't met half of their family. Also, if the player befriends Labelle enough, she will also start to share some past memories with them. Additionally, Labelle repeats things Mabel says such as, "You come back, now!", which Mabel says every time the player leaves her store. Labelle then stumbles and rephrases herself for a more elegant way to put it. If the player befriends some characters for long enough, they will tell the player that Labelle is the third Able sister, not naming her by name, but referring to her as a third Able sister who took a job in the city. She is the middle child of the family.
In Animal Crossing: City Folk, Labelle runs GracieGrace, as the real celebrity, Gracie, does not want to own a shop. Though GracieGrace sells more expensive items, Labelle says "it's a small price to pay for quality."
In Animal Crossing: New Leaf, Labelle is reunited with her family and now works at Able Sisters. She runs the right branch of the shop, which sells accessories. According to Sable, she claims that Gracie began to call her Labelle to make her name fancy while her real name is Label. However, Labelle stuck to the name given to her by Gracie.
Able Sisters Episode
The episode is a part of City Folk when the Able Sisters start to reveal that Labelle is their long lost sister.
Throughout the story, the player visits Sable and Mabel, Pelly (Once), Gracie, Tom Nook, and Labelle. They reveal the story of their lives. While Tom Nook, Pelly, and Gracie blurt out secrets, but they do tell more of the Able Sisters' lives. Labelle reveals that she wanted to leave to become a fashion designer, but Sable got into a fight with Labelle, and Labelle left. Sable wanted to stick as a family after their parents died and Mabel was too young to understand anything back then.
The player should then talk to Mabel when she stops following him or her around in Able Sisters. She will sigh, and the player can either say "What's wrong?" or "Back to work!" If they say "What's wrong?" Mabel will say she got a letter from someone in her past. Then, the player should talk to Pelly. She will tell him or her that Mabel is getting letters from some person. Pelly also says that she does not want to be nosy, but she also wants to find out what it is all about. After that, the player talks to Labelle when she stops following the player in Gracie Grace. She will tell him or her that nothing is wrong and everything is fine. The next day, the player talks to Gracie (who will be there, but not do a fashion check) and she will say that her life has fallen off the catwalk and Labelle says chic is a baby chicken. The next day, the player talks to Mabel, and the day after that, he or she talks to Tom Nook, and the day after that, he or she talks to Labelle. Then, for the next three days, the player talks to Mabel and then Labelle.
Names in other languages