Hi Lorna, thank you for this additional information. I'll continue to look further, but for now your setup did not provide a cue for the issue you are describing :(
Some other checks that could potentially provide cues:
1) Does the sidebar at the bottom only appear on your homepage, or individual post pages as well? For example, do you see the same issue on this page in Chrome: http://lornasvoice.com/2012/09/14/im-totally-cat-woman-in-an-awesome-not-creepy-way-part-3/ ?
2) Around the same time that the issue started appearing, did you change some design elements of your site, for example, changed your Custom Fonts under Appearance > Custom Design?