Amaterasu usually wasn't one to talk a lot, even if someone would understand her. But there were situations she made exceptions, of course. This was one of them, considering how kind he was being to her.

"I've been able to understand you the whole time", she barks. "I can understand human."

If nothing else at least the barks could be thought of as a yes, she thinks. Since she can't be sure if he can actually understand her.