There are three problems I noticed occurred in this film with the Duchess.
1. In the croquet garden, after the Cheshire Cat disappears, the Queen of Hearts sends for the Duchess. Notice that there are only a few lines between when the executioner goes to fetch the Duchess, and when he actually comes back with her! I know that this is Wonderland, but time doesn't change anywhere else in the film.
2. In the kitchen, when the Duchess is singing the song "Wow Wow Wow", she floats around the table in the center of the kitchen. At the end of the first chorus, the Duchess has completely gone around the table and is about to end at her original point while the baby sings "wow, wow, wow". Notice that when they get a close-up of the baby's head, the background is still moving. Yet, in the very next shot, The Duchess has turned the corner and stopped moving.
3. Toward the beginning of the second chorus, the Duchess begins to move, once again, facing the usual way. But, after a shot of the Cook and Alice, notice the Duchess has completely changed directions she was facing. She surely couldn't have done it in the time that was given.