I sympathize with you as you try to find best care for your mother. My friend who is 85 has had lung issues for the last 10 years. At one point she was diagnosed with MAC,. She did a cycle of the "Big 3" and got a negative sputum after 18 months. She was monitored regularly by Pulmonologist. A year later Mac came back. She did another cycle of Big 3 but ended it after 10 months. She did not see improved symptoms. Her lung scan showed pseudomonas. Next her doc suggested a course of injected meds which she could learn to give herself. She declined. Now she's been nebulizing saline and nebulizing Tobimyacin (separately). Tobi is one month on and one month off. She has not seen good results and dislikes the side effects. Coughing and mucus build up persist. Next week she visits her Pulmonary MD, hoping for alternatives.
Like your mother, she has had GI issues(constipation) and takes Linzess. She struggles to gain weight.
As she recounts her medical issues to me, I hear a series of "trial and errors" in finding what might clear up her lung infection. When seeking treatment, one important consideration is to weigh the "risk/benefit" because many meds have unbearable side effects.
Each person's condition is unique! I hope your mother's condition will improve.