We have been talking about this at
http://my.brandeis.edu/bboard/q-and-a-fetch-msg?msg_id=0000BDMacOS X comes with openssh. No GUI, but you might try a wrapper script around rsync. One script to rsync the production site to her Mac, another to rsync it the other way.
There is now an early alpha sftp GUI at http://www.macssh.com/
MindTerm 2.x has a very impressive ftp-to-sftp proxy in Java. You open a tunnel and point any old FTP client at localhost. Unfortunately the Java implementations for MacOS are pretty weak, but try your luck with http://www.mindbright.se/mindterm/