Sending a thank you e-mail to a professor as an external intern I'm new to Stack Exchange and I apologize if my etiquette on posting a question on this platform is "wrong".

So I took a course last year with a professor who was exceptional on her subject that gave me a better perspective on the subject, and ultimately got me a really good internship in the same domain.

How should I write her an e-mail (without being awkward) with a thank you note, as I wasn't in touch since the end of that course?
I think the proper answer is "Just Do It." She will be delighted to hear from you. Tell her about your current success. Open and close with "thanks". That's all it takes really. 

Of course the things you say here would be excellent to include in your thank you. 

However, sometimes a more formal letter is called for, sent by ordinary mail. That is up to you, of course.