From StrategyWiki, the free strategy guide and walkthrough wiki

Gracie is a giraffe with a real flare for fashion. She drives around the different towns in the Wild World. You will find Gracie parked in front of the Town Hall when she is visiting your town.

When you talk to her she will give you a fashion quiz. Make sure you have one letter slot free so you can receive your certificate for your fashionista badge. If Gracie disapproves of your fashion style she will give you a shirt. If you keep talking to her she will ask for donations to do a makeover. If you donate 5,000 bells or more her new look for you will include an exclusive Gracie fashion item.

These makeovers usually include a new shirt and an accessory. Gracie will give you the Moldy shirt if she really dislikes your style.

[edit] Rewards

Here is a list of the items you can receive from Gracie: