Glad your snake has been to the vet and it seems like things are sorting themselves out!
I just thought I'd share some pics of some facial swelling one of my snakes experienced. Same situation as you, it came on pretty fast. One day I had her out to show my friend and I kind of thought to myself "hmmm her eyes look kind of beady and small today" but didn't think much of it. Next day she looked like this:
The vet found no RI but said her inner upper-jaw looked irritated. He said to just keep an eye on it and see if any redness comes up in her mouth. He said she could have lost a tooth, got poked by a rats nail, been bit (which wasn't an option since she eats f/t) or maybe even was nose-rubbing. I put her in a different bin with less of a tolerance between the rack top and bin top and her swelling did go WAY down.
Also of note, her face does swell up quite a bit while she's in shed, but it always goes right back down.