Falls are the writer’s friend, along with gunshot wounds and car accidents, because whatever outcome your plot needs is entirely possible. People fall from great heights and live, and people fall from lower heights and die.
It's almost entirely on how you land, what you land on, and the height of the fall. People have died falling off a bar stool--what's that, four or five feet at the most?--and survived falling from aircraft.
I’m sorry to hear someone you knew thought ending their pain was the right thing to do. Please don't let yourself feel any guilt for not seeing her intention. She chose this.