I actually wonder if what set her off was something fairly innocent. Pintsize mentions to her offhandedly that he also uses a military chasis. Actually think of what that could do if she has a despair pit that deep. She sees this little robot, one that looks nonthreatening and at least somewhat cute, who is among people with no problems or fear, and then she thinks of her large military frame, the terror she inspires in others, and a mixture of anger and sadness makes her feel the need to leave.
Also looking back at it Bubbles may have been sabotaging the whole evening, Hannelore wasn't afraid of her but Bubbles made her uncomfortable fairly quickly. She came in violently and when Marten came back to talk to her trying to be polite she was passive aggressive and insulting to him. Her other reason for leaving might actually be a certain level of frustration, essentially rejecting them before they have a chance to reject her. Similar to how Faye would push people away for fear that if the did get close they might abandon her the way her father did.