Susan, the problem is that the "sort descending" option is only available after the thread has loaded. There are obviously good and sensible reasons for having "sort ascending" as a default, but the ability to choose a descending sort from the thread list pages would enable us to catch up with the latest additions without having to load the whole thread, saving time and bandwidth, and hopefully solving Alice's problem as well. Any chance Max? In the interim Alice, try the following.
Click on the thread name as normal, as soon as the "sort descending" option is displayed, click on that. This should abort the original load and start loading a reverse order download. As soon as you have got enough loaded to display the last few messages (Guesswork I'm afraid) click on the "Stop" button on the tool bar.
best of luck