"She eats food."
Translation:Lei mangia il cibo.
Lei mangia il cibo would infer she eats THE food ... which is not what the question asks for.
Mangia il cibo is saying "you eat the food" i think there is a mistake here.
It could mean both. Lei means 'you' (formal) and 'she.' They take the same verb ending, so mangia is still the correct verb. Presumably it would be obvious in context which you meant.