The book "Communion" (same a film's original title) by Frank Lauria. But it's the other way around, the book was an adaptation of the film.

what was the name of the book was qme4good love to know

Wow, TXs for that bit of info.
So now, the story does make a bit more sense (ie: where did Angela's daughter come from & who the dad was, etc).

There was a novel based on the film?! I did not expect that at all. That's neat, though, that after 20-30 years of watching this film, I finally picked up on that. Thanks so much for that info.
'Destiny is a fickle bitch.'
-Benjamin Linus

Yes. In the novel that was based on the film, that was the story. If I remember correctly, the daughter died of a brain tumor and Tredoni had a vision from St. Michael telling her to start punishing sinners.