well...most guys have this fantasy...very strange....because women don't have such a fantasy! I would be pissed if I see my boyfriend or husband have sex with another woman....but guys have this fantasy to feel that their wife or girlfirend is desirable by other guys!
She over reacted, just let it go and she will be okay....
My ex-boyfriend told me the same....and I got pissed, I thought he doesn't like me and he wants to use me....but then I told him what if I pick his best friend, and then he got so sad and for a while he kept asking me if I like his friend....hehehe....he was going crazy out of that....he even told his friend.....your wife should have done the same....hehehehe....
be relaxed and talk to her and tell her that this is just a fantasy, and that's because guys want their wife to be desirable by other guys....that's it...and you would be so jealous of thinking about it even!
take care
marjan