Can commenters of a post receive email notifcation when someone replies to their comment?

Hello there!

I have a social website setup for a client that allows people to comment on each others' books (they are writers and publishers) ...

My client received a comment on her book, and wrote a reply to that comment, but she received a comment notification that someone commented on her book.


The person who actually left the original comment didn't get notified of the reply to her comment.

Is there a way to set Wordpress up to email the author of the post of a comment, but then also email the author of a comment when they receive a direct reply to that comment?

Code snippets, plugins, I am interested in any way that can make the commenting a little bit smoother.