It din't sound like an overnight change. it's her choice but what I wonder what was her motivation to change.
If I had to guess, I think she had always had a seed of critical thinking in her. She did mention her father "was and still is a skeptic with a strong intellect and good native training in scientific and critical thought processes", so I can imagine this was always a part of her. Critical thinking is partly about questioning your established beliefs. As she said "when you start questioning these beliefs, there's a domino effect that eventually smacks into your whole house of cards".