Hedge Dying? Friends Question...

The trouble is that the leaf miner is inside the leaves so there is very little in the way of chemical treatment that can help. Your friend could try removing the affected leaves and then burning them. If the hedge is badly infected your friend could cut it back hard as privit hedges will respond to hard pruning - they should then feed the hedge well to make it strong enough to fight off future attacks although there is no guarantee this will work as privits are very prone to leaf miner.