You ate saying her face and not the side of her neck, right? My first suspect would be some type of dental issue and perhaps it is way in the back and you can't see it easily. I realize they have heavy coats but did you try slowly partying the hair so you can see Diwn to the skin to check fir injury or a possible bite?
I hate to assume anything about lumps, especially in a dog her age. When was the last time she had a thorough Vet exam? At her age. It would probably be a good idea to get those lumps and that swelling checked, get a blood panel done and a thorough dental exam. Is she eating?
Sorry, anything beyond that and I would just be guessing. Hard to recommend treatment with an unknown cause. Did the Benadryl help?
If this lump is right below the eye towards her nose, that's a classic sign of an abscessed tooth.....Yes, they can come up over night!!!!! The swelling does make it look like an eye issue, but it clearly is not!
Something else: This happened to one of mine & off we went to have her teeth checked....The lump came up overnight & her eye was swollen shut.....Turns out, there was a splinter lodged in the side of her face.....It was under the skin & broken off...I could not feel it.....Once it was removed, the swelling went down immediately.....We did give a short round of antibiotics because of the location......Let us know what happens......Karla