One other thing...
My mom has found the oral swabs (mint and plain) helpful since she cannot swallow. She has also tried a number of Rx "drying agents" but found that they make her mouth SO dry that it is uncomfortable. We found the plain swabs at our local pharmacy and I ordered the mint from amazon. She likes to dip the plain swab in cola or the mint swab in water. It certainly doesn't help with all of the secretions but this inexpensive remedy has helped with the terrible taste in her mouth.
If you haven't already tried a suction device - the Devilbliss Home Health Suction unit that Kiaser DME provided has been very helpful throughout the day and particularly after use of the cough assist.
Hope this information helps in some way. I'm sure your mom appreciates that you are looking for ways to help her feel more comfortable. I know I often feel helpless against this disease but I have found a wealth of information on this forum that has really helped.
Best of luck to you.