Seems unnatural to use wybór here. I would use decyzja.
Literal duolingo: decyzja- decision, wybór- choice.
Yeah, you're right. Wybor is technically a better translation for choice. It seems like an unnatural sentence in English, too, btw. Not a big deal.
Why not "To jej najtrudniejszy wybór w życiu". She only has her life.
It's a bit different, but... why the heck not, added.