The woman was fined with EUR 1,905 for leaving the dogs in the car and refusing to cooperate with the police, the local police said in a press release on Thursday.
She also verbally abused the police officers and other patrons at the bar after they started urging her to let the dogs out.
The 46-year-old, who took a third dog with her to the bar, went so far in her insults, threats and refusal to cooperate that she had to be restrained by the officers.
The police said that the dogs had been locked in the car for about half an hour. The car windows were lowered somewhat and the dogs were not injured, the police added.
Slovenia is amidst a heat wave, with temperatures well over 30 degrees centigrade in the shade.
Update: The police in Koper have now taken the woman's dogs away, as she refused to stop leaving them inside a hot car. Read more here