Weight and body oppression is oppressive to everyone. When you live in a society that says that one kind of body is bad and and other is good, those with good bodies constantly fear that their bodies will go bad, and those with bad bodies are expected feel shame and do everything they can to have good bodies. In the process, we torture our bodies, and do everything from engage in disordered eating to invasive surgery to make ourselves okay. Nobody wins in this kind of struggle.
Dieting was cruel; it was an abuse of human rights. Yes, that's what it was, and she should not allow herself to be manipulated in this way. She stopped herself. Thinking like that was nothing more than coming up with excuses for breaking the diet. Mma Ramotswe was made of sterner stuff than that, and so she persisted.