Thanks. The Unlimited Sidebars solution did not work for me because I only have one sidebar that I want displayed across the board (categories, subcategories, and individual posts) with the exception of one category and its posts. Using Unlimited Sidebars would mean that I would have to tediously assign all those sidebars (and I couldn’t figure out how to get the sidebars to display on subcategory index pages as well as individual posts within those categories).
In the end, I realized I was simply looking for a way to make posts under that one category to be fullwidth. I ended up using the Main Sidebar globally and manually setting certain posts to Fullwidth from the individual post editing pages.
Posting in case this solution helps someone else!