Well one way would be to upload a new file to the site and to the correct location with an FTP, although I'm sure people here probably know a better way...
Doing it this way, would let her edit content in a notepad.txt file, but there's no real way to control how it looks...unless placing it in a simple <p></p> would work.
<div id="clientcontent">
<p>
<!--#include file="clienttext.txt" -->
</p>
</div>
Granted if she wants to change the headlines and all that, you'd want a headline.txt then article.txt, or tell her the <h1></h1> has to stay intact to make her headline a headline...
Just a thought... probably not the best solution though.