Amanda wasn't even a suspect when she was questioned, the police had no idea she was in any way involved in the crime or knew who was. She wasn't even called to the station. They called in Raffaele because they wanted to speak to him alone. She insisted on going with him. While Raffaele was being questioned, since Amanda was there, they thought they may as well ask her some questions, so they questioned her informally in the police station public waiting room. Hardly iron maidens and thumb screws.
They became suspicious of Amanda because during his questioning Raffaele dropped Amanda's alibi and told police she'd left his apartment to go to Le Chic and he'd told them a load of rubbish before because Amanda had told him to. Then, when asking to look at Amanda's phone they saw the text to Patrick, when hitherto she had told them she hadn't sent or received any messages that night. The message was written in a way that in Italian meant she was going to meet the recipient of the message that night. When they asked her who it was to, she broke down in tears and started hitting herself in the head saying over and over 'It's him, it's Patrick, he's bad, he murdered Meredith'.