Thanks davmerit and RossMitchell for your replies! Yes, this makes sense. I think I’m going to go with a sub-domain. I get the impression it would be more tidy, rather than placing a directory amidst all of my current files.
A follow-up question about databases. I’m very unfamiliar in working with them so I try to be very careful when I have to touch them in any way. When I’m ready to upload the new design, what is the best way to get the most recent copy of the database from my wife’s live site into the new sub-domain?
If this scope of this question is too large, any links you know to helpful sources would be appreciated, too. Thanks!