Hey, when you're tired, you're tired.
"Personal Trainer" ✣ is a four-page short story set in what appears to be Agatha's future, roughly concurrent with "Agatha Heterodyne and the Electric Coffin". Castle Heterodyne is as safe as it'll get, is cleaned up and repaired, and Agatha and her associates travel the countryside troubleshooting and shooting at trouble and being shot at.
One morning, after a long night fighting lizard cult guys, Zeetha arrives at Agatha's bedroom to wake her for training; Krosp warns her it might not be as easy as she thinks... and when they find her still strapped into a fighting-augmentation exoskeleton-like gizmo... well, as they say, "hilarity ensues".
"Personal Trainer" was published online in May 2006 (page descriptions) in the middle of Volume VI, and (re)printed in Volume VII, Agatha Heterodyne and the Voice of the Castle.