Could be a number of things, but the most common and probable cause would be respiratory infection. Right time of year when its cold and they get too cold. In some cases just raising the temperatures in her enclosure, can be enough to reverse and get rid of it, but in many cases RI can be stubborn and your snake will require antibiotic treatment. It certainly won't hurt to make an appointment with a reptile-orientated vet to get her checked out. Vet can do a mouth swab to confirm bacterial infection and give you a course of treatment for him. In the meantime, I would crank the heat, if it isn't already. Put a hide box over her heat as well as cool end so she can thermoregulate and keep warm. Give her maximum heat, and in her cool end you need to add another heat source on a thermostat set at a minimum temperature to stop it going too cold.
A question for you? Is she yawning or look like she is gagging? If she attempts to regurgitate, this will fill her mouth with excess spit. They may not be a problem at all, but for the cost of a consult with a good reptile-knowledgable vet, you can save yourself a lot worry and time having to try and save a snake that could very well be ill. Our vet did a talk at one of our herp meetings not long back and suggested that by the time ppl spot the symptoms (drooling, bubble blowing, wheezing and noisy breath), the snake can already be in advance stages of RI. So acting quickly is critical to help your snake recover.
