选D,即使是当她不知道要怎么说的情况下,她的话也比其他人的更可信.
逗号不能连接两个完整的句子,前面的.Even when she didn't know是让步状语从句, what she would talk about是宾语从句修饰know,
Even when she didn't know（ what she would talk about）,she spoke more authoritatively than most people did.
这里她不知道将要说什么,话还没有说,说话对于know来说是将来的事情,用将来时,如果用C则表示她不知道已经说完的话,呵呵,已经说完的话要是不记得,那估计是她记忆力不好啦~希望对你有帮助!