My child went on her first international assignment at 11. Tbh, that's not the stuff i worry about, but GB have a good system in place where she started weekend, 2 night training camps at 8, and slowly built up. She and i both know the coaches, other athletes, and more importantly the chaperones, and feel just as comfortable as if she were going away with a friend.
What we find stressful is the day to day stuff. Is she in the right club to get her where she needs to be? Too many hours, too few? Would she be better with a different coach? Communication is notoriously difficult for parents and most of the time we have no idea of the plans or goals for her. We actually took her out of a very successful, high hours club as we felt the environment was toxic, and would only get more so, even though she was doing incredibly well there. Which was and is very scary.
You invest so much in sport, financially and emotionally, to have that pressure that any action we might take will change everything, it's huge.