Originally Posted by: pdmassmail

The notation in fact adds a C, but the B is still there, and this also seems to be what Lisa is saying to do. Is this a mistake, or am I missing something? How did we go from a "sus" to an "add." Thank you.

You've got the right idea. I think that was a small oversight by Lisa. She's trying to include as much material as possible, so she shows that voicing as an option to add to the open G chord.

To be clear:

Gsus4 is: G (1st) - C (4th) - D (5th)

Gadd4 is: G (1st) - B (3rd) - C (4th) - D (5th)

Hope that helps!