That was one fact thhat she wanted to withhold from him.  She didn't want Eren to hear that, as well, righton top of everything else.  But now, he had and Kate said nothing when his eyes searched her for some kind of confirmation or denial.  It was better that she didn't speak.  She'd already said that he seemed berserk and even in a daze.  It couldn't go worse than that.  Well...except for the fact that the MPs wanted him dead.  Stupid, short-sighted idea...  People were already calling the Battle of Trost the first human victory over the Titans.  They'd stopped the Titans from crashing through the second wall.  They couldn't just kill him.  He was too important.

Hence, the plan...  Katherine had no idea what it was.  She hadn't been told anything, and nobody had had the chance any, since she'd been doing her job, down here.  This was all Sara's game, at this point, or rather it was Captain Erwin's.  They were gonna find a way to keep him, to battle the titans and maybe retake Wall Maria.  Just think...  If they could take that all back, and then somehow take on the Titans who caused it all...  Not only would that be a great human achievement, but they might finally get some answers.

At any rate, Eren seemed to believe Sara's words - something in the way she said it or that powerful look in her eye - and he agreed to...well...basically hang in there, really.  All he could do was not go flipping mad and turn into a Titan or something.  That'd get him killed.  Katherine was going to wait until the two of them were out of earshot, though, before asking what this plan actually WAS.