Drinking water, and keeping it down ios a good positive thing so far.
If she were my dog, what would I do? I would call the vet, preferably speaking to the vet who did the surgery. I would make an appointment for her to be checked, and not necessarily wait for the regular post-surgical check (unless that is scheduled today or tomorrow.)
When is her first routine post-surgical check due? It usually should be within 5 days, very often on the 3rd day...
But definitely call your vet for advice. The vet may need to examine her.
What temperature is she running? That is important. A dog's normal temperature can range from about 101 degrees to 102 degrees. Anything above 102 is a fever, and that could signify some form of infection.
Just as we do, they all react differently to anesthetics. Some people are nauseous or vomit after surgery, although many do not. It's the same for dogs.
It is also possible that the post surgical pain has managed to 'get a foot in the door' -so to speak, and it has become a vicious cycle...as she can't tolerate food so her belly aches badly....and she can't take her meds...
A dog who is in pain usually refuses food. Her hard breathing/panting could be caused by pain.
A pain shot -possibly with an anti-emetic also added might set her to rights. And that will mean taking her in to see the vet. I would speak to the vet and take her in as soon as you can.
I hope she will be much better soon.
It's important she doesn't get dehydrated, so do be very careful to watch that she IS drinking and keeping it down in the meantime.
Update: she started drinking water but still no appetite