yeah, they can give her a shot and clear it up. I had that problem years ago with a Red tail Boa. Sneezing, Wheezing, Bubbles around her snout, and she was less active than normal. So I took her to the vet, and they gave her a shot. She was better really fast. Completely cleared up in about 3 days.
I agree with sian.kelly, 28% Humidity is very low. Try to keep it at 50. Also, 66 degrees is low too. Some people will say it's ok since your snake can simply go to the warm spot if he wants to. But I've read several "Corn Snake Care" books and pamphlets that all tend to say Temps should "Never" go below 70 degrees. For that very reason, I installed a secondary heat pad on my tank because it gets cold around here. I have the secondary heat pad on the cool side and it kicks on if the temp drops below 71. If the temps are above 71 it does absolutely nothing. I try to keep my warm side at 85, the cool side stays around 71, and there is a zone in between that hovers around 78. I also have a "Humid Hide" in the cage. The humid hide is simply an enclosed box with a hole for the snake to crawl in and out. It's filled with sphagnum moss that has been moistened with water. The moist moss allows moisture to permeate throughout the cage raising the humidity a bit. Also the snake can crawl in and enjoy the moisture if he wants to. Some people use Humid Hides during shed cycles as it helps keep the skin soft. But I just leave my Humid Hide in there all the time. Rufus seems to like going in it from time to time.
You can also move things around in your cage a bit. Sometimes simply placing your water bowl over the heat pad will actually boost the humidity 10 to 30 percent.