SHTML is a good way to go.
To use it, you could just name the files .shtml
Then, include the content you want to post with a statement like this:
<!--#include virtual="topic.txt" -->
You can just show her how to ftp the files up using Windows Explorer. (not IE)
If you want to get fancy, you could add some PHP code to allow her to edit the files on the server through the web, but that will create some potentially serious security issues, and may not be worth the effort.