The closest would be: "A girl is having a meal." 밥 usually carries the connotation of a regular meal, not just food. Also, "A girl" is a better choice than "The girl" here. It is because of a rather intricate differences between 가/이 and 은/는. In short, 가/이 is used often for mentioning something for the first time, corresponding to "a". (Although it is difficult to say for an isolated sentence like this)