She has infection in her stomach. She is 11 y.o Maltese and she had fever for entire day. I took her to the vet and they gave her antibiotics and told me that tomorrow she has to have a surgery. She is breathing heavily and I am worries that she might not make it. Her fever is down, still has it. Is there any way I can make her breath slower. They said no water from now until morning for surgery.
Breathing heavily can be a symptom of many problems. It can be a sign of difficulty getting enough oxygen, pain, anxiety, a result of metabolic acidosis possibly secondary to the infection that you are seeing, the feeling of being uncomfortable, a number of other conditions or even a combination. Metabolic acidosis is described better here:
There is no way to know how serious your dog’s condition is without seeing it and the best care would be given by a veterinarian that can give your dog an exam and advise what the best supportive care options are. To do this, I would recommend having your dog taken to an overnight care facility. Some of the options they might be to give respiratory support, possibly intravenous fluid therapy to balance the electrolytes and pH as well as monitor the vitals of your dog until it is time for surgery. As you are worried about your dog not making it through the night, I would recommend this as the best course of action.
Otherwise, if you just want to help your dog remain comfortable, you could try to support your dog’s anxiety which is described more in this article which may or may not be of benefit: