I don't know why Adam is trying to downplay Sheila's religious beliefs in order to back up the idea the bible was planted was Jeremy. Since he had already established by his genius forensic observations that Sheila could not have found the bible in a house that big 
Well my question on page one was 'did Sheila know where the bible was' ?
There was a strong possibility she did not.
In her psychotic rage, shooting four people in the head, and smashing Neville's head in, there was also a strong possibility she wouldn't remember where it was. Or not even bother to think about using it.
But of course she had a read, before putting the bible onto her own blood. Before shooting herself. Twice.