The key is to (without blame) identify the fears.
I was raised with a STRONG personal faith in God.
Still have it-and still poly.
I read an article on lovemore.com in the last magazine they had on there. It was about the Bible, God etc.
Where does it say that GOD SAYS loving more than one person is WRONG? (clue, it doesn't)
The critical part of maturing in our lives is the point where we look at all we've been taught and we dissect it in order to identify what IS true for us and what IS NOT.
Sounds like your wife has hit that time, it's not easy-but it's VERY worth looking into.
Also-a lot of people seem to have a REAL personal struggle with worrying about what "everyone else" thinks.
I suggest two books-neither are about poly-but they pertain to relationships and ourselves.
Living Happily Ever After-Marsha Sinetar
The Seven Levels of Intimacy-Matthew Kelly
Great real life suggestions for resolving the issues that cause us to let fear control our actions.
"Love As Thou Wilt"