Fiona's Pony Race Children's Book

Fiona is in a racing fever: she first wins twenty euros at the racetrack. Then she has the brilliant idea of organising her own pony race on the riding school! Everyone is enthusiastic about the plan, only Johanna is grumpy. What’s wrong with her? The next morning the whole race track is destroyed, which the children have painstakingly put together. Fiona is sure: this can only have been one person...