"She is at school."
Translation:Dia ada di sekolah.
You don't always have to use "ada," you can also just say "dia di sekolah." It's the same thing. You should know that, Duolingo.
Hai! Many sentences in the course can be accepted with "ada" and "berada", those verbs are lacking in the most of sentences. So, I think the contributors already know "that". Please, try helping with the course reporting your sentence.
Selamat belajar! :)