I'd recommend this book/pamphlet
The Cautious Canine
I'd also use methods found in The Dog Listener by Jan Fennel. I wonder if they have tried having him just completely ignore the dog for a week or so, no looking at, no talking to, no trying to make friends at all. Sometimes for a fearful dog, this helps them relax and come up on their own and they feel safer and less threatened. If he did this for awhile and then she began cautiously approaching to check him out, I'd still have him ignore her and maybe have
her (the owner) toss her a treat when she approached, and gradually move that over to him tossing the treat but not looking at her and ignoring her still. Just continue in this way until she seems comfortable in each situation, i.e. glancing at her and then tossing the treat, waiting till she gets closer, eventually holding out the treat without looking at her until she takes it from his hand, and so on.
I have found with Tasha, who is very suspicious and fearful of men other than my husband, that if I can get them to just ignore her she will relax and approach them after awhile, sniffing. If they turn their attention on her she backs away and gets frightened again. I find that the more they try to coo at her and make friends with her, the more upset and frightened she gets. If they hold out a treat she gets even more suspicious and agitated. It could be his attentions are actually making things worse right now.
The above method is what I'd try in that situation. It will take time and patience but I think it has a high chance of succeeding. Good luck and I hope any of these ideas may help!
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