It had never occurred to her that it was wicked.

If, as Mrs.Munday explained, it was the Devil that had whispered it to her, then what did God mean by allowing the Devil to go about persuading little girls to do indecent things?
God could do everything.

Why didn't He smash the Devil?
It seemed to Joan a mean trick, look at it how you would.

Fancy leaving a little girl to fight the Devil all by herself.

And then get angry because the Devil won! Joan came to cordially dislike Mrs.Munday's God.
Looking back it was easy enough to smile, but the agony of many nights when she had lain awake for hours battling with her childish terrors had left a burning sense of anger in Joan's heart.