Tip:
Add chord symbols automatically.

The issue:
You need chord symbols in your chart for the rhythm section. You have forgotten most of second year music theory.

Solution:
Using one of the Plug-ins, Sibelius will analyze the chord structure on a grand staff and put the chord symbols in for you.

With the existing music in a grand staff selected, go to the Plug-ins menu and select Text> Add Chord Symbols.

Remember, the Plug-ins in Sibelius are NOT undo-able, so Save the file BEFORE applying the plug-in, so you can revert back to it if this plug-in gives you unexpected results. However, generally the defaults work fine. Just click OK in the next dialog window.

The chords appear according to Sibelius' analysis. Notice that the default behavior is to only place chord symbols in your score if the chord name has changed, as in standard notational practice.