Answer:
Hannah is simply experiencing what is known as ego depletion. This entails that her self-control has been drawn from her limited pool of resources that can actually be used up and hence Hannah used too much will-power to control herself from eating the cookies and eating the radishes instead and she has used up that will-power on that in such a way that she cannot persist at the anagram task.
Step-by-step explanation:
Hannah is simply experiencing what is known as ego depletion. This entails that her self-control has been drawn from her limited pool of resources that can actually be used up and hence Hannah used too much will-power to control herself from eating the cookies and eating the radishes instead and she has used up that will-power on that in such a way that she cannot persist at the anagram task.