I've done as she suggested, created a child theme, and made alterations to the "layout" section in the stylesheet.
However, after making that change, the text content in the widgets is now indented more than I'd like. If you look at Christine's original design, the content in the standard widgets such as the "recent posts" one is indented just slightly. After my dimension change, the content is indented a great deal more.
(As a side note: I also noted that when I added a text widget even before I created the child theme and made the sidebar dimension changes, text content wasn't indented, and actually spilled over into the left margin. I roughly managed that in my "contact" widget by centering the text content. I don't know if that challenge is relevant to this discussion, but I've watched enough episodes of "House" to believe it's always worthwhile to include any anomalous behavior, just in case.)
I'd like to keep my wider sidebar, but with Christine's original indent for widget content. If anyone has any recommendations on best practices to achieve this, I'd be most grateful. Thanks.