This was my first thought when I brought her to the veterinarian. At first I thought she managed to bump her head somehow and for the first month or so I took photos once a week to see if the swelling was going to recede. When it wasn't, I took her to the vet. He looked at my album and came to the conclusion that the swelling would likely go down. He opened her mouth and looked inside and saw nothing. Said her lips looked kinda big and her body condition needed attention. Gave me some liquid ointment to rub on her mouth once a day with a cotton swab. Nothing really changed with treatment. Her lump remained the same size until the day it suddenly deflated and left a hole behind on the top of her head. Unfortunately, selection for exotics veterinarians is limited so second opinions were difficult to obtain. Because her behavior was normal and she didn't seem bothered by it, I assumed that it was a feature she'd have forever and I just sorta shrugged it off. Every time she sheds the spot where it opened up changes a little bit. At first I was concerned that when she would shed, that the wound site would need assistance to properly evacuate the scab tissue but it seems that it rectified itself properly and as time has gone on, the hole became a scale and it's just really wrinkled in shape. If there's interest, I can grab the DSLR and take some pictures of it with the macro on.
I agree that this was likely a close call. I wonder what the "right" thing to do for her was. How would a different vet expert have handled this if she were their patient? I suppose I'll never know. Ultimately, I'm happy she's seeming to do very well and eating healthily for me now. She's a very kind, easily handled snake, has never exhibited a temper and is a pleasure to watch in the evenings.