Hi, I can help you with your question today.
I wonder if she had some type of trauma that we are unaware of to have the swelling progress so quickly.
Another possibility would be an insect bite or sting.
When you are back online, please post her weight for me.
We can try a dose of antihistamine as well as some pain medication for her.
I do not think this is an emergency, I think you can wait until morning to have her evaluated at your local vet.
Great. You can try 50 mg diphenhydramine OR 10mg loratadine OR 10 mg cetirizine for the antihistamine.
For pain, you can give 250mg acetaminophen every 12 hours for pain.