Joan's background is unknown, but she has told the player she had been selling turnips for sixty years. She appears in town before 12 noon in every Animal Crossing series so far. In Animal Crossing and Animal Crossing: New Leaf, she sells White Turnips. White Turnips, however, sell for a different price depending on Stalk Market. The Stalk Market is a play on the existent Stock Market in reality. More than one can be bought a week from Joan. Players can ask Tom Nook (Reese in New Leaf) what White Turnips are currently selling for at two different times of the day, which will have different prices and he will buy White Turnips between Monday and Saturday.
In Animal Crossing: Wild World and Animal Crossing: City Folk, she continues to sell White Turnips which work the same way as they did in the original games on every Sunday. She now also sells Red Turnip Seeds for 1,000 Bells which will need to be planted like flowers, and be watered each day so they can grow to their full potential and later sold to Tom Nook for profit. Forget to water them one day and it wilts. This cannot be fixed. Red turnips require constant care. However, the player needs to be early to catch Joan and get a red turnip. Sometimes there are none. Only one Red Turnip can be sold to the player(s) each week.
Joan can be asked to explain her store and turnips, but she wishes not to explain how her store works. However, she does not act gloomy while explaining. Some villagers also explain that the player can buy them in bulk and go to Tom Nook's to sell them for a profit on a certain day. The player must not go too far ahead, though. After a week the turnips will expire become spoiled turnips, and are therefore useless.
Along with Farley, Luna, and the player (In the Happy Home Showcase or in a Dream Town) Joan is the only character to have her own unique voice. Her voice is much lower and gruffer than that of the rest of the female characters, which leaves her mistaken as a male character.
Joan always tells the player no matter how many years they have been playing, that she has been selling turnips for over 60 years, she still mentions this in Animal Crossing: City Folk, even if the player has been playing for ten years, or have time traveled. This may be because she says over sixty years, which covers any number of years beyond sixty.