I'm not sure I should tell you. [While she did not attack the walls or the people as directly as the Colossal and Armored Titans did, Annie was still to him very clearly an enemy of humanity. She sided with Reiner and Bertholt. She killed countless soldiers. She nearly kidnapped Eren. Even though her plans failed, Armin holds no sympathy for her. It goes without saying that he does not trust her either.]

...I will say I'm not alone. I wouldn't try anything hasty; retaliation will come down faster than you'd think. I don't see how it would benefit you either.