You could give her a card and write your thanks inside. Some cards are truly beautiful and meaningful and ad a nice touch to your handwritten message. Or you could give her a handmade card if you can make one yourself, or one custom-made for you (I'd suggest still handwriting your note, it's a nice personal touch).

I also want to say, as a poet myself, if a client gave me a poem as a thank-you gift I would appreciate it a lot even if it weren't my favorite style or very well-written. It's a truly beautiful gesture - especially from someone who doesn't normally do it but made an effort for me.

Those are really great gift ideas you already have. Good luck!