God has indeed preserved His Word and I have several good English representations of that Word in the Geneva, KJV, NKJV, NASB, NIV, ESV, HCSB, ect.
Well, you can say that till the cows come home, that doesn't make it the truth.
Amy has demonstrated by her own experience that the NIV misled her to believe it was a sin to be angry for any reason. And the answer you gave above is silly, I guess if a person wanted to be a nit-picker they could argue that it is only a sin to be angry at your brother, but it is not a sin to be angry at your sister or your parents. Or if you want to interpret "brother" to mean a fellow Christian, then it is a sin to be angry at a Christian brother, but it is quite alright to be angry at non-Christians.
Nonsense.
Words matter. When Jesus said those who are angry at their brother "without cause" are in danger of judgment, he meant just that. It is a sin to be angry at someone without a just cause, but it is not a sin to be angry at someone for a just reason.
If being angry for any reason is a sin, then Jesus would have been a sinner when he overturned the moneychanger's tables and beat them with a whip.
And this is what bothered Amy, she saw an inconsistency. She believed that Jesus taught it was a sin to be angry at your brother for any reason, and then read that Jesus was very angry when he chased these moneychangers out of the temple. This made Jesus seem to be both a sinner and a hypocrite.