Mabel is one of the three Able Sisters, co-owning a tailor shop with the same name with her quiet sister Sable, and later also with her sister Labelle. Mabel's task is to assist customers with their purchases.
Mabel has been raised by Sable as a child, and doesn't know much about her biological parents. Mabel also didn't know much about the existence of Labelle until Animal Crossing: City Folk.
An amiibo figure of Mabel exists! For more info about this amiibo, see this page.