The horse owner from Bad Bentheim had already carried the pony around 100 kilometers when police noticed her unusual passenger, reports Süddeutsche Zeitung (SZ).
Officers stopped the car close to Hanover – and opening the boot, freed the animal from its tiny enclosure.
Despite the woman having covered the car boot with straw, it was far from an appropriate means of transport, reports SZ.
The woman had been heading to the Czech Republic with the animal, but was forced to cut the journey short.
Officers took the pony to the police station in nearby Bad Oeyerhausen.
It's not yet known whether the woman will be charged with a violation of the Animal Protection Act.