So here is the update, and I must say I'm a little embarrassed.
Chiro had to reschedule, so that didn’t happen as planned (he’s coming next week anyway). In working her during the week, I noticed that the area in question wasn’t really acting normal. For example, she would be in a sweat from working but a circle about 8 inches in diameter in this area of her neck would not look sweaty. Or if I bathed her, that same 8” circle would appear and not look damp like the rest of her. So I started desensitizing her to touch in the area. [I think it’s important to note she is in summer coat, with very short fur] Once I got her to where I could really touch the area, I noticed that there was a very slight roughened area under her coat. I took my fingernails and scratched it, and she had a fit like it hurt.
So, back to the wash stall with betadine. I washed her thoroughly, and took a very soft silicone scrubber and softly worked the soap into this area. Gradually very small black “chunks” (about the size of a pin head) began working out of her fur. Nothing large like a real scab, but little chunks of “grit.” She wasn’t totally happy about what I was doing, but she didn’t react like it hurt at all. I worked on it for a pretty good while, and then coated the area with an aloe antiseptic.
The spot is not totally gone, but has reduced in size to about 2” in diameter. Her fur when wet or sweaty has gone back to looking like the rest of her neck, and I’m continuing to clean the area each evening.
What I think happened is she must have slept lying down on something that caused either an allergic reaction or created a surface infection beneath the outer guard hair of her coat. The “something” then contracted when it dried when she was standing, creating the ‘corrugated” look I show in my initial post. This must have been pretty irritating as she would not let me touch it and she really reacted like it was painful.
When the Chiro comes out next week, I will provide an update if he finds anything wrong with her cervical alignment.
Thank you very much to everyone who helped, offered an opinion, or just support. It is wonderful to have a place where one can ask "silly" questions that are worrying them and get real, meaningful answers.