Well, sort of, and not really. She's having preventive surgery at 22 for a cancer she doesn't have and may never have. She has a 10% chance of never getting it. Sounds a tad extreme to me. Seems she could hold off until at least the kids are born and nursed.
10% means one chance in ten of NOT getting it, and as other posters have pointed out, breast cancer is very aggressive - it nearly killed my mother at 30. Assuming that the test is reliable (always a big if, granted), I think her decision is rational, if heartbreaking.
Why should she play Russian Roulette with 9 full chambers and 1 empty? Perhaps declining to play the game is really better.
She had something very unimportant removed that had a 90% chance of threatening her life.