3.6 update on a mac

Is her blog on a live server? If so, she does not need to install anything on a local computer. If she wants to install WordPress on a local computer, she has to first set up a server environment – see:

http://codex.wordpress.org/Installing_WordPress_Locally_on_Your_Mac_With_MAMP

But the local installation of WordPress won’t be connected to a site that’s on a hosted server.

A few more details might be useful in sorting out the problem – i.e. what is the site URL? Where is it hosted?

Looks like her site is hosted on BlueHost – see:

http://www.whois.com/whois/thelettereblog.com

For updating info: http://codex.wordpress.org/Updating_WordPress

I’d strongly suggest making a full backup of the site before updating:

http://codex.wordpress.org/WordPress_Backups

As to why content has disappeared, not sure. Standard troubleshooting would be to deactivate ALL plugins and switch to an unmodified twentytwelve theme to rule out plugin or theme problems.