The cow had escaped from her field near Quickborn in Schleswig-Holstein on Wednesday, and wandered into the woman's garden – where she spotted what she thought was another cow also on a midweek jailbreak.
Enraged, she charged into what was actually her own reflection in the window of the woman's house and crashed through the double glazing, police said on Friday.
Passersby who saw the smashed glass called the police, who arrived to find the cow calmly chewing cud in the kitchen with just a few scratches to show for her mix-up.
There was glass all over the floor and the window was completely destroyed – but the woman who lived in the house was not at home at the time.
Police officers rang a local vet to help them coax out the animal out, who had made herself at home on the kitchen floor. The initial plan was to tranquilise her and drag her out of the house, the Die Welt newspaper said on Friday.
But being sturdier than the vet had calculated, the injections only annoyed her and she galloped out of the door compos mentis into the neighbour's garden.
It was there that the vet managed to sedate her and she keeled over, asleep, into some shrubbery.
She is now back with her herd and has fully recovered from the ordeal, while repairs are being made to the house.