Leash aggression is not uncommon, and it may well be that she feels you will protect her if need be, but she's not so sure about your fiance.
Here are a couple of good articles by Suzanne Clothier which address both leash aggression and the underlying issues that often lead to it:
http://www.flyingdogpress.com/onldagg.html
http://www.flyingdogpress.com/sayhi.html
(Lots of other great articles from Suzanne can be found at http://www.flyingdogpress.com/artlibreg.htm)
Here are a couple of good articles by Suzanne Clothier which address both leash aggression and the underlying issues that often lead to it:
http://www.flyingdogpress.com/onldagg.html
http://www.flyingdogpress.com/sayhi.html
(Lots of other great articles from Suzanne can be found at http://www.flyingdogpress.com/artlibreg.htm)