It's so sudden, that's why it's hard for the family to accept

I talked to her the day before she was sent to hospital, and she sounds so energetic and positive about her treatment plan.
To me one dose of chemo killed her right there and she didn't stand any chance to survive.
It's almost definitely certain that she'd still be around if she didn't have it.
I understand that the limitation of modern medicine, but just want to have an answer and closure so we can face her kids' question on what happened to their mother.