The manure sprayed across the road, covering the 26-year-old and her convertible Mercedes.
Police described the incident at midday on Wednesday in Traunstein, southern Bavaria, as "particularly tragic”, the Münchner Merkur newspaper reported.
The road was closed while 25 firefighters and specialist cleaners went about clearing up the mess caused by the manure shower.
According to police, the trail of manure stretched back for one kilometre.
Train travel was also affected as a platform near the road had to be closed while it was cleaned.