She hasn't read this book yet.至今她还没有度过这本书（强调没读这个动作由过去一直持续到现在）
yet 仍然,通常要跟完成时连用.
She didn't read this book yet.
yet 放在这里不合适.一般过去时,仅仅表示发生在过去的动作,跟现在没有影响.
应该改成 She didn't read this book yesterday（或者last week）等过去的时间.