Scarlett is the toughest Beauty to win over, but she doesn't require gifts. First off, you must unlock all 20 of her Challenges by locating her throughout the Episodes. Once you've unlocked all of her Challenges, you must then beat them. I highly suggest waiting until you have both the Dark Booster and Ulti-Mondo costumes equipped as it will make the Challenges much more smooth. For extra comfort, play them on Easy Mode. After you've unlocked and beaten all 20 Challenges, Scarlett will not be able to contain herself anymore, she and the achievement will become yours.