You mother is at best place to be if she needs to be hospitalized to find out what's going on. I had severe Mucositis just from chemo, which was one reason for my hospitilaztion back in 2009. As Uptown mentioned, mucocitis can effect mucous membrane throughout the body, and affected my lips, mouth, throat, esphogus and stomach. There are different grades, 0-lV, and mine resulted in being NPO, abbreviation for a Latin phrase, "nothing by mouth" for several months, and was just on IV, and didn't have a feeding tube. As far as the thick mucus, I had that too, but don't know it's relationship to Mucocitis, which has different phases of initiation to healing, and may be part of its process or salivary gland dysfunction from chemo or others. The hospital used the Aspirational suction machine to get the mucous, fluids out, soft sponge tooth brushes to clean the mouth, rinses, plus others measures. Later on I used mucenex, for mucus, and nystatin for the infections, which can occur from ulcers, so cleaning the mouth is important, besides being on systemic antibiotics.