Final answer:
Jenny is likely in the preoperational stage of Piaget's cognitive development theory, characterized by egocentrism and an assumption that others share her likes and perspectives.
Step-by-step explanation:
Jenny appears to be in the preoperational stage of development according to Jean Piaget's theory of cognitive development. This stage typically occurs between 2 and 7 years of age. At this time, children display egocentrism, which is the inability to understand that other people have different perspectives and feelings. Since Jenny believes that others will like the same food she likes, simply because she likes it, it demonstrates a classic example of egocentrism common in the preoperational stage.