Dear Jean,
I wanted to write you a note to thank you. I am sorry that you felt disappointed that your work responsibilities were not what you expected. I have enjoyed having your assistance with my projects.
Although the tasks we handled were not as varied as you would have liked, just think about what you and I have accomplished since September. We organized the annual small business conference, updated the association's web site, and answered scores of inquiries, many in great detail, from business owners who needed advice on a range of topics: loans, benefits, licensing, etc.
I feel the year has been very productive for both of us. You've been an congenial and conscientious assistant and all of us have the highest regard for your abilities. Please feel free to call upon me for a recommendation if you require one for future employment.
Best of luck,
Thomas