No parent causes this. Adult cancers build over decades of exposure, and that's the work I spend my life on. A 2 year old hasn't had those decades.
In kids it's almost always random, a mistake in a fast growing body, not diet, not anything on a label. Nara did everything a mother should, including trusting her gut the second something looked wrong and getting Whimsy seen fast. That instinct is the whole game. Most children come through this now. Pulling hard for that little girl.
i believe in re-reading and re-watching your favourite books & movies at different stages of your life. the plot never changes, but your perspective does.