Although there are some cases in which certain Victoria’s Secret models do have a specific routine, such as diet and excersize, this is not universal. (See below). Also you are asking for Victoria’s Secret-grade type models, not the actual models themselves. There is no specific diets that models have that any other health conscious person does.
One great example of models not dieting in any specific way is Cara Delevingne. Cara does not diet and actually loves fast food. She has McDonald’s for lunch and pizza for dinner during Victoria’s Secret Fashion Show. She says that she is skinny and therefore needs to eat a lot, just as I had to do. In absence of frequent meals she feels weak and faints. To call it a diet, you could say she eats a full and well balanced diet and opts for more proteins. On occasion she feeds on fast food only. As she is skinny and lean she does not cares much about the extras calories of fast food