MBK spit up foamy saliva. RI?

[dextrose]

My ~7-month-old MBK was crawling around in her tank as per usual. She opened her jaw and I assumed it was a yawn or jaw stretch. She did it again but this time, spit-up foamy saliva. There are no other signs of an RI. No excess saliva around the mouth, weight loss, lethargy (she was a bit less feisty today maybe that was the lethargy), wheezing, nothing. I'm planning on monitoring her for a couple of days. Could she have an RI? She hasn't eaten for about 6 days so I don't believe it was any type of regurgitation. Her hot spot is about 87-89 Fahrenheit and the cool side is about 73. She has 2 hides on each side of her 20-gallon tank, 3 plants on the corners of the tank, PVC pipe for her to hide in, and 2 branches of wood she likes to climb on that help her shed. I cleaned her cage and disinfected everything with a half water half vinegar solution as well as replacing all her substrate. She is my first snake and I fear I am killing her somehow.