There is a slight gap in the left hand corner....it doesn't appear to ever fully close. I haven't examined it in detail- and I can get some better macro pictures later today. She's a recent WC. Thanks!
It could be any of the things that Stefan mentioned. You can try cleaning it with peroxide and see if it heals. I would keep her on paper towels until you can see if it is healing. I know you are in MA and I would say that if you are near the Tufts vet school there is an excellent herp vet there by the name of Dr. Jorge Mayer. Otherwise I have been very disappointed in vets that say they treat reptiles.
I have a girl that had something similar and I could not find anything wrong. I did clean her with peroxide and it may have helped. She is eating very well and acting her normal self. Her mouth did not gape open as much as your snake's does though.
Well... it don't look like mouth rot. If you just noticed this overnight, it might me the she has something stuck in her mouth (like a piece of substrate or something).
I don't see much of a gap in that last photo. (The little "hole" in the front is always there, that's where they stick their tongue out.) If she's recent WC and she's been that way since you got her, it could be she had previous trauma (e.g. broken jaw) that's just healed a little wonky. Best to get someone with experience to look at her, obviously. But if you can get a good look in her mouth and you don't see an open sore, swelling, or any foreign objects, AND she's eating OK and has a normal attitude, it probably wouldn't be wrong to just take a bit of a "wait and see" with her.
I would suggest, though, if you do wait and see, that you start up a little "medical chart" for her - record everything she eats and how easily she takes prey, observe her attitude twice a day, try to get a weight every couple days, etc. It takes snakes so long to deteriorate, it's easy to think everything's going OK and then suddenly realize one day that you've got a very sick snake. If you're keeping a detailed record it's easier to notice a downward trend early on and get her to a vet if she needs it.
one of my snakes seemed to be doing that one day and it freaked me out at the time
in her case I think it was just a facial expression though
let us know whether yours keeps doing this long-term
rhea "you cannot depend on your eyes when your imagination is out of focus" Mark Twain
It's difficult to tell from the 'cloudy' photograph, but in the first pic there appears to be an area of white inside the mouth, in which case I would be inclinded to agree with Stefan and suspect stomatitis.