Dear hazu,
Phrenic nerve paralysis can result as a complication of surgery. The diaphragm on the side that was damaged will not generally move with the other diaphragm. Oftentimes the patient is asymptomatic. There are no treatments that I am aware of for phrenic nerve paralysis other than time.
I had a condition where my phrenic diaphram was 'stretched' and paralyzed. I underwent surgery and the diaphram was slit and a 'tuck' taken in it. This allowed my internal organs (liver, colon, etc.) to be placed in their proper locations instead of against my heart. My diaphram is still paralyzed, and will always be. The end result is that I can not forceable exhale from my right lung. With my pacemaker, I am still able to bike, swim, run, lift weights, and play golf. My times are slower, but that is mostly due to the PM.
The paralyzed phrenic diphram should cause no noticeable problems for your aunt.
We only use a portion of our lung capacity anyway.