“It’s… I did some things I don’t want to talk about right now.” Because it’s clear from his urging that he doesn’t know.

He doesn’t know she was willing to kill herself. He doesn’t know she was going to murder Luffy in his sleep. He doesn’t know and… that’s fine with her. The less he knows now, maybe the conversation will be easier for her later.

“I don’t think they’ll trust me.”

That’s all she really needs say about the atrocities she committed.