It’s great that you and your friend enjoy the same books. And it’s natural to want to talk about other things with her too. The next time she talks about the series, you might share a few things you also like about it. Then you could mention another book that you’ve read and ask if she has read it. If she has, you can talk about it. If she hasn’t, then she may want to read it.
If she steers the conversation back to the book series, you might gently change the subject. In a nice way, maybe you can say “I know how much you like these books, and I like them too, but can we talk about something else for a while?” Then you can suggest a new topic to talk about.
Art by: Keith Frawley