Thanks Doug! I know this program. I've even bought a license for it. It's indeed pretty good, but it's not a true solution to my problem.

I want SWMBO to be able to manage her own iPhone's mp3 files using her own Mac.

This is possible already, but it's made more difficult for her because the search doesn't seem to work in Finder. So she can't search for specific tracks now.
I'm guessing this is one of those stupid issues that's easy enough to solve, if you know how. Google hasn't given me any answers to this problem specific.