Is it normal to include a thank you mesage to a teacher

I ended up improving from a 3.4 to a 3.7 in a class curved at a 3.0, partly because my instructor helped me out at the tail end with stuff like working with an extra credit assignment rewarded to only the top 3-5 student papers of 49. At the end of the quarter, she asked us to include some book resale information in an email and I thought I'd attach this:

[instructor's name],

Thank you for your generous help this quarter. I truly appreciate your willingness to work with my extra credit assignment as well as your clear and detailed explanations to my other questions. In the end, it was a direct reason why I able to improve and exceed my goal for this class!

[book resale information]

Thanks again,
[my name]