Do you believe with a mother like June that Sheila had never read the Bible ?
In 1985 most people were educated about the Bible and religion ...
Sheila was a self confessed white witch - are you aware what that means Adam ?
She believed her children were possessed by the Devil - you think she was not interested in religion ?
Her previous breakdowns were based around religion Adam ...
I'm sure Sheila would have read the bible -or had it read TO her- at some point.
SOME were bible educated long before 1985.
You seem not to know what a white which is. White witches are esoterics involved with nature, herbal healing, astrology, numerology. They aren't involved in mainstream religion.
The "Devil" thing with the children, when she was ill, was probably a throwback to when June called her "Devil's child". It was probably, at he most vulnerable, her greatest fear.
It's reasonable to assume that fear would play a dominant part in mental illness.
This particular fear seems not to have been a major part of her 1985 breakdown.