Sarah has started in motion the process of moving the site registration from the old host to a new site registration thingie. After that completes, the DNS will need to be propogate to the new location. After that, Sarah will go through installing drupal on the new site. When she transfers the database to the new site, she will shut down the old site.

What this means is that there will be periods during which the site is inaccessible to some people or to everyone, depending on the vagaries of the DNS propogation and the reinstallation. However, since the new site will go up at the same time that the old site is finally turned off, so long as you can see the site and post to it, you can be confident that your posts are actually being stored and will not be lost in the transfer.