Wouldn't it depend on what else she's eating that day, what she has with a sandwich, what she's doing etc.
If she has a decent breakfast, has something with the sandwich, isn't being particularly active, has snacks and isn't having to wait until too late in the evening for dinner, then it's probably fine.
However, if she had a crappy cereal breakfast, is spending the day hill walking or it's her main meal of the day, then probably not. She may also be quite hungry due to growing/puberty.
Isn't the point that she has what's probably right for her? Although a lot of the time, sandwiches as food aren't particularly great options, depending on what type of bread and filling it contains (I know MN sandwiches are made from home made wholegrain seedy bread and filled with chicken salad, but the reality for a lot of people is more of the processed white bread filled with ham variety).