The English is pretty good.
A few minor edits (the changes are bolded
Thank you for the
beautiful flowers. They are gorgeous and I really appreciate your kindness. I not only enjoyed the
flowers, but also the delicate vase. I shall for
ever remember this gift as one of the most precious things in my life. I hope to have the opportunity to reciprocate sometime
. If you ever have time to visit me, I would be very happy to see you.
again for your lovely flowers. Please give my kind regards to your family.
Do you and Lucy share a common culture? (Chinese, for example?)
If Lucy is Western (American, British, etc.), I'd encourage you to take things down just a notch. It's a bit much to describe a vase with flowers in it as "one of the most precious things in my life," and that might ring false to Lucy. You could say, perhaps, "I shall forever remember your thoughtfulness."