Defeat Rio with a blackjack (Ace plus any face card). This will make her available to partner with in the game. Her favorite color is hot pink, and her preferred food is Ice Tea or Ginger Cookies. It will take a lot of gifts to get her to like you enough to partner with, especially if you are playing as Christie. After you partner with Rio, Zack will give you a gift that tells you of a special "Challenge." This challenge is to defeat Rio with another blackjack. When you do this, a message will pop up that tells you that Rio is now a playable character.
To unlock the "Private Paradise" option on the main menu, complete the game once (full fourteen days with your first character). This will allow you to view any of the single player relaxation cinematics from the game that you have already experienced while playing on Zack Island.