All the other office chairs have headrests while Essex's doesn't. So the story is like this:
Due to being treated as a joke too much, Essex has become depressed and taken to drinking away her troubles. After Shangri-la confiscated Essex's usual chair by holding it up out of Essex's reach, she's absolutely gobsmacked that Essex somehow found a second headrest-less chair in the office to joyride on, and is busy wondering where said chair could have been stashed in the office (neglecting the one she's holding up) when the Commander walked in and saw them.
...Shangri-la has some work to do to correct the lies and slander about how she's a tosser.