My niece is plannning to visit from Greece for a month. Since i cannot take so many days off

i was thinking to enroll her in a school in order for her to learn German (actually that was her idea). She is only 10 years old and i was wondering if there is any school to join in order to learn German and also spend some time during the day (half day will be enough). she is already taking some German lessons at the moment but still very basic level
Cheers
D