Sorry to hear about your Mom.
What age group is your Mom?
Has your Mom had other chronic health problems in the last few years besides the mucus lung problem?
Is she able to do the huff coughing with airway clearance techniques considering all you have said?
It sounds like your Mom's Body Mass Index is low??? Building the BMI up is hard sometimes to do, but so very important....It goes along with keeping the immune system strong, as you probably know.
Wish there was a magic wand to help your Mom and us with all that she/we have to concern herself/ourselves with in dealing with it all, it isn't easy and especially hard when trying to get under control multiple concerns.
Hope suggestions given in this Mayo site will help.
Wishing you both all good answers that you have questions about.
Barbara

I’m so sorry your family is going thru this. I have not been on big 3 but know from my time here that sometimes the meds and med schedule is modified in order for patients to tolerate it better. You might discuss that with her physicians.
Is the saline hypertonic? Many of us use 3 or 7%, preferably 7 since it’s thought to inhibit bacterial growth. It helps get mucus out. That is another thing to consider.
One other thing to help with weight is to maximize number of calories in every bite and swallow even if using cream and other things considered “not healthy.” We used to say “no free liquids” meaning every swallow had calories.
Good luck to you. It’s so hard to watch family suffer.