You will have to go to the pictures location in finder. Once there copy out the photos to a folder. Then move it to your wides iPhoto and you'll be able to sync them. That's about the best way I know unless you point both iphotos to the same photo storage.
Is your iPhone 4 synced with iPhoto? Is the folder you want to put on your wife's phone in the same folder in iPhoto? If so, just plug in your wife's iPhone, go to the photos tab, hit sync photos, select the folder and sync. Then, she'll have all the same photos in the same folder as on your iPhone. Hope this helps.
There's an app I can't remember the name of(?), that allows files to be transferred between iPhones on the same WIFI network. Wonder if that would work? Would probably cost a few bucks, but might be useful in the future if you have more than one iPhone in the family. Just a thought.