Haha. Uh, I don't really have head canon for that... but I suppose I could make some now! "Persistent insubordinate behavior" could mean almost anything, couldn't it? She was always one to have her own way of doing things. Her own Cain-inspired leadership style. It's easy to see her popping off at a "martinet" if he insisted on doing something that was clearly not in the best interest of the ship and its crew in any given moment. And, of course, it's easy to see her proceeding to do it in the proper way.

I'm sure she was frustrated... perhaps ashamed... that after everything they'd been through, after everything Cain got them through (and how she did it) to be left with someone like Gardner as her heir. Brought so low so quickly.