I am 69. At 50, my doctor discovered I had been living with 2/3 of my right lung inoperative. I had always played golf but at school and elsewhere, running or walking uphill tired me quickly. I could do 36 holes of golf a day...walking at normal speed. I now find I have good endurance but if I walk uphill, my pulse, normally 66, shoots up to 125 in less than 50 yards. I use the treadmill at the gym 3 - 4 times a week and can do 60 minutes at 3.1 to 3.5 MPH and 1 - 4 per cent uphill grade; my pulse gets to 130 and averages 113 yesterday. I weigh 230 lb; do not smoke and never have; have found I walk more slowly than 10 years ago and now really hate uphill walking. I use a sleep apnea machine at night. MY view? Living with 66 per cent capacity is manageable, but I hate to think what would happen if I did not exercise at the gym each day.
One lung, for me, has meant no limits on what I can do (except long distance running). Sometimes it makes getting a chest cold more uncomfortable but honestly, besides people asking if I have asthma, no one can tell a difference. And at the end of the day, I have no recollection of a life without one lung.
Your child is only "disabled" if you raise her to be. However, if you raise her challenging her to TRY everything and DO whatever she sets her mind to, her lung will be up to the task and she will figure out what she is comfortable doing. Best of luck!
Remember, having only one lung is not a "disability"! Your child will tell you when they cannot handle the activity... please don't constantly remind them of their condition, just let them try things and figure out what they like to do physically. The body is an amazing, adjustable thing.
Side-note: the only medication I have had to take for my lung is a rescue albuterol inhaler (more for allergies but as it dialates the bronchial tubes I mention it here). That is all.
Best of luck!