Wallace told Heat that the model and socialite wanted to use a shop-bought jar of pesto in her pasta dish.
Asked who was the best cook, Wallace said: "Since they won it? Lisa Faulkner. At the time of winning? Phil Vickery, closely followed by Nadia Sawalha."
"The worst was that model, Victoria Hervey. She wanted to make spaghetti and pesto using a jar of pesto."
He added: "From the series you can expect to see us break down the façade of celeb and turn these people into normal contestants. That, for me, is the thrill of Celebrity MasterChef.
"If they get through the early stages, they just want it so badly. They stop being celebs and start being MasterChef contestants."
Co-host John Torode said: "At times we see the best cooking we've ever had, and at other times we see the worst. It's real extremes."
The full interview appears in this week's Heat magazine, on sale now (Tuesday, July 31).