In this case you can just leave the "die" off because it is girls in general. If you would ask for one girl in special it would be "das Mädchen". In the singular case you couldn't leave the article off because it would be a very weird sentence otherwise. I'm sorry, this is very difficult to explain even for a native German speaker like me. Maybe someone else will do better...
You are right mikelucas, the fact that words like "Mädchen" look the same for sing and plural can be confusing. Nice explanation Vreny! English speakers can also think of it this way: "Does she like girls?" but not "Does she like girl?" The singular requires an article like "the" in both languages.
Thank you for replying, I understand ( I think). Maybe when I get better at the German language it will become easier.