Exactly. Not many people use a batch of blueberry muffins as a romantic gesture but it still gets the intended point across and shows that you're grateful.

The thing that you wrote in your first post on this topic is what she needs to hear. Not:

thanks for your help throughout the session

but more like:

Nobody else has been there for me this past year and I was headed down a dark and miserable path but your being here this year helped me feel that I was someone worth putting effort into. You have given me a gift that I will never forget.

That is the best gift you can give your teacher.

You keep trying to put the value in some material gift but those words are what she’s going to value.

I’m just going to say this: if you give her a card that says “Thanks for your help this session” you will have missed a beautiful opportunity. DO NOT give her that generic “thanks” message.

I was the guy who warned you about the chocolate being interpreted as romantic. But a far worse danger is going through life missing the opportunities to create beauty.

You have an opportunity to create something beautiful and meaningful for this teacher, and you’ll only achieve that by articulating exactly how she helped you.

Believe me when I say that, for adults, meaning is the thing we crave and lack in our life. Muffins can be obtained at the grocery store. A true, well-articulated and vulnerable communication of the way one has had a positive impact in another person’s life is a treat most people hear maybe once or never in their lives.

I know it’s hard. But you did a good job of explaining her positive impact in your original post. All you need to do is re-state that while addressing her in a note, instead of us.