Your poor mom. That coughing is exhausting. Is she bringing up a lot of mucus with the coughing? Has the amount or color changed which might indicate an infection? Has it been cultured recently including for MAC? Is she using a flutter valve device like aerobika or Acapella then huff coughing after she does neb and vest? That seems to help people who produce a lot. Answers to these might guide answers from those who’ve dealt with this a longer time.

If no sign of infection and she’s huff coughing already, think about post nasal drip or reflux as possible causes of the cough.
Good luck to you both.