You do this with the "ln -s" command/option.
Let's say you created your girlfriend's account with userid hodsonsgirlfriend and created a subdirectory named "shared_ftp_for_hodsonsgirlfriend" in her home directory.
Log into *your* account using ssh and change to the area where you would like the folder to show up - say ./home/hodson/hodsondesign.com/uploads".
Type the following. Don't forget the "." at the end:
ln -s /home/hodsonsgirlfriend/shared_ftp_for_hodsonsgirlfriend .
This creates a symbolic link to your girlfriend's directory. The webserver should be able to read this directory. You will not be able to write to this directory. It's like creating a "shortcut" to a folder in windows.