You can do one of Illusen's quests every twelve hours. Once you complete one of them, you cannot do one of her or Jhudora's quests for another 12 hours. Listed below are the rewards Illusen gives you for completing her quests. Also, since these are quests you request, you're able to use the shop wizard for finding items.
You can win an avatar from this game! Well, in face, two!