She considers the question, both whether she wants to answer it or not and what it is in and of itself. She's not the detective he is, except in the sense that he had called her one, which really is the only way she needs. She's enough of a detective. She understands the important parts.

That that would be the first question--

Either the Joker has done something horrible to her or horrible to him. And he is almost certainly dead in his world. There's a way that people say the word 'dead', even if the sentence doesn't actually intend to tell you whether someone is or not. That was one word, one inflection, the body language around it, she'd learned well before the others.

She knows what the Joker did to Barbara, after all. She knows enough, has seen enough of the videos, looked into enough to know that the Joker is one of the worst. It hadn't ever really come up, but she knew that if there'd been a mission to deal with the Joker, her Bruce would have sent her away. And that, perhaps, she would have understood.

Perhaps.

Her answer is a single shake of her head. She could provide the basic information he'd requested.

"What did he do to you?" is her real answer.