If she were my dog, I would call an emergency vet and ask about this. They can usually advise you whether this is something that is normal in a bite wound. If the swelling is really bad, she may not be on the proper antibiotic, and that may need to be changed.
How big is the wound? You say she was bitten on her head? But you say that the swelling is under her skin on her head and neck? The infection could be spreading, and not to alarm you, but she could be getting what is called lymphangitis, or cellulitis, which means that the infection is spreading and could cause septicemia (blood poisioning or infection).
I am not a vet, but I have seen infections in both animals and humans that have spread, and she may need to be seen sooner than Wednesday. If you think you can wait, I would definitely get her seen tomorrow, but if it looks very red, and is swelling that quickly, you need to take her to the emergency animal clinic in your area. She may need an injection of a different antibiotic, or need to be given fluids if she is getting feverish or dehydrated from the infection.
Did she by any chance get any sub-q fluids when you had her to the vets? That can look like a swelling in the neck, where they usually give the fluids, near the neck, usually in the shoulder area.
Also, are both of your dogs' vaccinations up to date? Especially rabies? You would be best to call the emergency vets and ask about this swelling. If you can, you should also have someone help you take your dog's temperature rectally, and see if she is running a fever. Is she eating or drinking okay? Going to the bathroom okay? If she is very tired and lethargic, I would certainly have her seen as soon as possible.
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God bless and hope your dog is gets well quickly!