Pray, and be there for them in their time of need.
Special Children are given to us to show us our capacity for love and compassion. Even when they are with us briefly, they are always in our hearts.
God be with your friends and their child.
I agree with this. Love and cherish her during what will certainly be a very short life on earth, and comfort each other in your grief with the knowledge that she will be whole in heaven. My prayers are with these suffering parents and their baby.