Not really, no. The Desktop is a special folder in the file structure of Mac OS X, so other than leaving aliases on the desktop and keeping the files in the volume you wish, there's really no way to do this.
If you want to keep user files separate from the OS X volume, consider just moving her home folder to another volume and then allowing her to keep her desktop as messy as she likes.
Just to note, filling up your desktop with tons of junk can, and will slow the system down. Everything on the desktop is treated as a windowed object. The more there is, the more RAM the OS has to devote to keeping track of it.
If she must have this stuff on the desktop, then have her separate items by a few logical folders and then put all of the items in them. Then there are only a few objects directly on the desktop.
I use aliases on my desktop--folders and separate files--organized by categories across the top and down the right side. When I download files from the bank I put them in the center till I enter them in Quicken, then they go in a sub-file in an alias of my accounts file (top, left). I have a DragThing Disk Dock on the desktop with a Desktop folder on it. When the files on the desktop suddenly disappear, I just click this folder and they show up in their usual places.
Thanks for all the suggestions. Since it appears that I can't set up a real* Fake-Desktop (looks exactly like a Desktop but files are stored elsewhere), I've decided to try out a fake Fake-Desktop (FFD, looks similar to a real Desktop).
- Name the folder (or volume) where files are to be stored: Desktop.
- Make it fit the whole window and set to Icon view.
- From View, hide all the bars (Status, Tool, Path, Sidebar)
- Use Show View Options to set the background.
- To force this window to open at login (just in case it is closed accidentally) use System Preferences > Accounts > Login Items
Voila – an FFD. Looks a bit weird to me, knowing that it covers the real Desktop and that instant access to disks and bars is lost, but Jenny almost never uses those things anyway. If I can't convince her to get more serious about using folders and hard drives, I'll see how she goes with an FFD.
*Talking about real Fake items reminds me of my time in Singapore in the 1980s when the touts in Orchard Rd would pester me about copy watches: "You want buy copy watch?". So I'd look at their wares for a minute or so before declaring: "Hey, this isn't a real copy watch. This says Rolex! I want one that says Copy Watch". Our little interaction would usually end with them rather annoyed and telling me something like: "You stupid!" That particular tout wouldn't bother me again.