Final answer:
Susan's difficulty with speaking despite understanding spoken language indicates that the frontal lobe, specifically Broca's area, was damaged during her head injury.
Step-by-step explanation:
Based on Susan's symptoms of having difficulty speaking but showing an understanding of what is being said to her, it appears that the area of her cerebrum that was damaged is Broca's area. Broca's area is associated with the motor commands necessary for language production and is located in the frontal lobe. This region is vital for speech production and is generally located in the left hemisphere, which is responsible for language in about 95% of the population.