Natalie McArthur, 44, left the female Yorkshire terrier, Crystal, who belonged to her father, and three other dogs in the closed vehicle as temperatures hit 25C.
Stirling Sheriff Court heard that the car was parked at the Burghmuir Retail Park in Stirling, and the dogs were trapped in the deadly heat for more than a hour on July 18 last year.
Crystal became so hot her body temperature registered 42.7C and she contracted hyperthermia.
McArthur, of Calton Crescent, Stirling, pleaded guilty to one charge of causing unnecessary suffering to animals. Her not guilty plea to a second charge of leaving three more dogs locked in a car the next day, outside a veterinary practice in Glasgow Road, Stirling, was accepted by the prosecution. Her daughter, Caitlin McArthur, 19, was also charged with causing unnecessary suffering to animals by leaving the four dogs, including Crystal, in the car on July 18, but her not guilty plea was accepted.
Sheriff Kevin Veal deferred sentence until October 3, to be dealt with along with other matters.