Although she made a few glances towards her cousin, who was sitting right next to the teen, Sara nevertheless listened to Eren, as he seemed to express good-will for the actions that she made towards him. Something had always been quite absolute amongst the Scouts: Trust, as it had always been a good asset within the battlefield, up to the point where that trust was mandatory amongst the ranks. It became one of the reasons why the Scouts were so upheld on their belief to take back the world that humanity lost; it was what kept them going. At the same time, it even extended towards those people that were considered "family", in Sara's eyes, whether or not, there was a relation. That didn't mean, however, that she would go out of her way, and reveal the one secret that she, Levi, and the Commander knew. Sure, there may be well, in fact, another Titan-Shifter before them, but that didn't mean they would let the cat out of the bag, just because the other showed up. It may, as well, come, and show up, at the right moment. That alone, was Sara's decision. 

Also, she had to assume that the price of Eren losing the deal, would end up with upmost defeat...mainly on the boy's part, and therefore, Sara was going to have to be discreet, and do as much as she can to keep him in the light of his power. However, it wasn't going to be an easy feat, considering that it would conjure suspicion for the rest of the recruits, probably with the exception of Erwin and Levi. It was one of her inner ideas, while the other leaned towards the lay-low: Just sit back and let Eren figure it out himself. It was a dilemma, considering that the teen was now technically her responsibility, and that he was the key for her to piece together her forgotten past. The thought itself caused the lieutenant to look over at Kate, who was in the same state, as her own Aunt: Wild and eager. Should she even mention to the young woman her issue? Can she even trust her word, even if she were indeed to tell her? Narrowing her eyes in thought, while continuing to keep eye contact upon the other, the platinum-haired woman remembered that Kate knew Eren and his friends, more than anyone in this very room. 

Their custody of Eren began right now, but then, they were to move out with Levi's squad, first thing tomorrow. 
Closing her eyes, Sara could only think of so many ups and downs for the very expedition.