Oxo, glad that your friend can still use Reiki. I invoke Jesus Christ whenever I use Reiki but no-one bothered to ask me what I thought about where Reiki comes from. The assumption was that it was from 'somewhere other than God'
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That said, I'm both
and
that your friend was told not to use self-help and visualization. There is nothing in church doctrines that bans either. Visualization can be creative (which is the kind athletes or singers use before a big performance or event) or guided (which is the 'imagine you are on a dusty road' kind of thing.) The first simply wires the brain for a good performance. The second is really useful for gaining insight and I've seen it used loads of times in a Christian setting. A typical example would be to get a group of people at Bible study or prayer group to visualise that they are walking to Emmaus when 'the stranger' appears and starts talking to them. Each person has to imagine what Jesus would have to say to them, and how they feel when they finally realise who he is. It's a really good way to identify issues around faith, your past, problems that you have now, all kinds of things, and get insight as to how to deal with them.
That said, visualization is sometimes used in Cosmic Ordering/Law of Attraction which can appear to resemble witchcraft to some extent so I can see why that might make church leaders warn someone off CO and LOA. But normal visualization? No.
As for self-help books, there are some which are very Christian (the Rob Parsons book sspring to mind) and those which have no religion at all (Michael Neill's for example). There really isn't anything in any of them which can be called unchristian and I would question why a church would tell people not to read material which may make them more self-reliant.
I'm glad for your friend...God sometimes works in ways we don't always expect. Have you heard the old joke about the man who is drowning? A boat comes past and someone throws him a line, but he says, no, don't worry, God will save me. Next a big ship comes, but again he says, no, don't worry, God will save me. Finally a helicopter flies over and they throw down a winch. No, no, he says, God will save me.
Eventually the man drowns. He gets to heaven and says to God, why didn't you save me? God replies, I sent a boat, a ship and a helicopter, what more did you want?