At the end of a shift, the player can choose an upgrade for the D.C. Diner. One of those upgrades is the Hostess. Once acquired, the Hostess will instantly welcome any guests to the diner and show them their seats. Once the tables are full, though, she will stop letting guests in until seats are available.
On the island, the Hostess only appears walking around on Main Street, in front of the Reverie Lounge. Before you climb on the train, she'll tell you that they only allow very important people on the train. After the island is over, she'll tell you she never would have suspected Mlle. Moreau as the thief.
The Hostess next to the Reverie Lounge
The Hostess on the upgrades screen
The Hostess waiting for the D.C. Diner's next customer
The Hostess also appears in a Daily Pop Sneak Peek called "Cast of Characters".
On D.C. Diner, the Hostess has a mole and wears a black dress. On Mystery Train, her mole is gone and she wears a puffy maroon dress.