i can only speculate that she didn't want to tell anyone her plans incase of an imperial spy telling them that they are going to secretly escape the ship, because that is when they are most vulnerable.
Also you are a leader of the entire rebel troops, you have to stand strong. If Gny. Sgt. Hartman had his subject question him and question his authority, he would act like a jerk and tell to stop asking questions and follow orders
That still is a pretty foolish plan, as that logic goes both ways. Her silence personally made me think that she was the imperial spy.