Alice,
Your letter is a great example of the perfect query letter: clear, succinct, and to the point.
"When the agent or editor opens your envelope, he wants to know what you have that he can sell. Tell them what you have in the first sentence or two. You want a conceptual hook in as few as words as possible. Use the skills you've practiced in boiling down your story to a high-concept premise for your synopsis and verbal pitches (you have practiced this skill, hmmm?). Get to the point immediately. Classify your work as to category and genre. Tell the agent/editor exactly where it fits in the scheme of commercial marketing."
http://www.sormag.com/queryltr.html