I have no reason to believe they were asking her questions about her whereabouts, her actions and her phone calls until she was in the interrogation. I'm sure she offered all that information as a matter of fact over the course of the four days, but since the police's initial theory of the crime did not include Amanda, they would have no reason to ask her about those things.
Having been the first to arrive in the scene, she had more information than anybody else about what the condition of the house was when she got there. That in itself would probably require quite a few interviews. As I understand it, she and the other roommates also were asked to provide names of anyone who knew Meredith, so they could also be interviewed.