Hello, I'm Dr. Deb and will do my best to help you today.
I'm sorry for this concern for your dog but it's a good thing that she's still eating and drinking.
I have several thoughts as to what might be going on with her:
1. She's been bitten or stung by a spider or insect. If that's the case, then over the counter Benadryl (Diphenhydramine) should help. The dose is 1 mg per pound of body weight twice a day. Sedation is a possible side effect.
The swelling should start to resolve or lessen within a few hours although some patients may take up to 24 hours or so before the face looks normal again.
2. She could have an infection, possibly stemming from one of her teeth. If that's the case, then she may need oral antibiotics dispensed by a vet before improvement is seen.
Over the counter Aspirin may be of benefit to help reduce some of the swelling. As long as your dog isn't vomiting nor currently taking any steroids or non-steroidal anti-inflammatory medication, then the dose would be 1 mg per pound of body weight twice a day, with food to avoid stomach upset.
I hope this helps and that her face returns to a more normal appearance quickly. Deb