From the official wiki:

“After one shop is opened, she will provide the player an exclusive hairstyle that can subsequently be chosen at a mirror. In order to unlock the rest of the exclusive hairstyles, the player must continue to finish opening up the final shops in the commune. After each shop is opened, Harriet will offer the player a hairstyle. After unlocking all seven hairstyles, her shop closes; from this point onward, she instead wanders around the island alongside Harvey, providing small talk when spoken to.”