Michele - You can widen either Sidebar to reveal long field/column names, or long category values, by un-freezing the default width and dragging the Sidebar width wider (or narrower) to suit the value lengths:

Toolbars > {Sidebar} > Other options > untick Freeze sidebar width

Notice that this will widen all Sidebar devices uniformly, not necessarily the best use of space. If you have only a few filter devices that have long field/column or category value names, consider adding a Device View and moving these wider filters to the Device View, which can be positioned anywhere on the tab, any size or shape, and is independent of the Sidebar(s).

Long field/column and category value names occupy too much horizontal space in general...consider using Field Organiser and Search/Replace blocks in the DataManager workspace to systematically shorten incoming field/column names and category values as much as possible.