Ruby emailed her instructor a question and he replied to her immediately.

What is your question?

To determine whether Ruby's instructor replied to her immediately, we would need more information, such as the timestamp of Ruby's email and the timestamp of the instructor's reply. Without this information, it is not possible to definitively say whether the reply was immediate or if there was a delay. However, if Ruby received the instructor's response shortly after sending her email, it could be considered as immediate.