I have heard of such stories like this countless times.. iguanas are strange critters for sure. It might be her smell, color of her cloths and hair.. or her general reaction with the ig.. I can give no easy answer. Nannette visits this forum and she has been in your wifes shoes before. Igs have been known to try to eat peoples hair if people use fruity smelling shampoos..
How does your wife react to your ig? Does she hold her ground or back off? If she is backing off have your wife toss a towel over the ig. The ig needs to know who is the alpha at the same time its a trust relationship so you have to find a balance. You could try holding the iguana and have your wife try feeding it a peice of fruit.. a cabob stick works to feed just use the dull end and make shure the ig does not eat the wood.
Overall you need to be careful... iguana bites can be painful and leave permanent scars.