The foundations of Bibi's low self-esteem were mainly laid down in her Microsystem.
Explanation: The microsystem refers to the immediate environments in which individuals interact, including family, peers, and school. Bibi's experiences with her family members (such as her sister's negative comments and her brother's embarrassment), her peers' bullying in school, and her relationship with her Life Orientation teacher all contribute to the development of her self-esteem and body image, placing the origins of her low self-esteem primarily in her microsystem.