One possible version:
Dear Miss Yan,
I am glad to have a chance to write a letter to you.I like you very much because your classes are so
interesting.But I want to give you some advice.First,you speak too quickly in class.Would you mind speaking
more slowly?Then we can understand you better.Second,would you mind not giving us too much homework
every day?If we spend too much time on homework,we won't have time to relax ourselves.Last,I feel you are
a little strict.I am a little afraid of you.Of course,you can still be strict with us in class,but after class we
sould be friends,don't you think so?
Yours,
Li Hua