From Nookipedia, the Animal Crossing wiki.
Sable (あさみ, Asami) is a character in the Animal Crossing series, co-owning the Able Sisters tailor shop, one of the two stores that can be found in the player's town. She is a shy, reserved character that prefers to work in the background while her younger sister, Mabel, assists customers.
Sable is a brown hedgehog with pink freckles and sad, shy eyes. She has no visible mouth, so instead talks by moving her nose. She wears a pink and white gingham apron and has a head full of large, spiky bristles. Her birthday is thought to be November 26.
Sable's life is very focused around the world she grew up in- she is happy with the slow pace of the country life and has proven to be firm friends with others from the village, most notably, Tom Nook. When Sable was only a young girl, her parents died, leaving her to care for her younger sister. She reminisces frequently of her parents, often sharing stories of her childhood. It is not known how her mother and father died, but it is certain that Sable was very unprepared, having to mature quickly and sacrifice her own happiness for that of her sister. This lowered her self-confidence and made her the introverted adult she is today. After her parents' death, Sable took over the family business and taught herself to embroider and make clothes.
Sable maintains the same role as in future releases of the game. She can be seen sewing in the corner, keeping quiet and secluded. If you keep talking to her she will start becoming your friend and sharing memories about her childhood. Sable also has a younger sister Mabel, who helps run the shop, and another younger sister named Label, who owns the Gracie Grace shop in the city, but changed her name to Labelle and stoped working at the Able sisters to live her dreams of owning her own store after Sable and Label had a fight. (Sable will eventually get sad in early January and explains what happened.)
In Animal Crossing: Wild World, Sable has a very similar role as she did in Animal Crossing. She is never seen walking around the shop, because she is always using her sewing machine. She doesn't say much unless the player becomes friends with her, but this takes some time to do. Talking to her everyday increases the chances of her revealing information about herself. At first she will say things like "Ummm... who are you?!", but when she is friends with the player she will say things like "Welcome! I'm so glad you decided to pay us a visit..." She watches a soap called Pointed Love, which she will comment on every Thursday.
 January Blues
In Animal Crossing: City Folk, Sable's role remains unchanged. After speaking with Sable everyday for 6 days, she will eventually stop ignoring you and pushing you away, but will make comments about the day of the week and sometimes tell you stories about her past life and childhood. Eventually she reveals a family secret--she is eventually forced to admit that the worker in GracieGrace is indeed her younger sister, Labelle. Sable does not get along with her sister as she feels that Labelle abandoned her to go to the city when their parents died, leaving her alone to look after Mabel.
 Other Appearances
Sable appears as a trophy and will occasionally appear in the background of the Smashville stage.