Hi, Sarah! I haven't come across something for a twelve year old, but for those with young children Dinolingo has very high ratings. It offers lessons followed by dinosaur themed games. I hope this helps someone!
If she’s looking for book-based. I am loving teaching out of Beste Freunde by Hueber. All the audio comes in a free app. German courses published in Germany for foreign language learners are called Deutsch als Fremdsprache. They have many good resources if you can wade through the German.