The first thing that comes to my mind is, if you're worried about editing yourself to protect old T, why do you think you wouldn't do that with her old coworker? You'd likely feel the impulse to edit negatives with her, too, to either protect your T or yourself from her disapproval.

Setting aside whether or not the old coworker would think it ethical, I would worry that re-entering your old T's circle would make things harder, as well.