Dear Teacher(或放她的名字比如Ms.Lee）,
I'm so happy to have you as our class' English teacher.I really hope that I can have an opportunity to learn from you, as my English is very poor.
We have had many teacher who taught us English before, but I think you can help us to improve our standard of English.I would like to thank you in advance and hope that we can get along happily during your tenure here in our school.
Yours sincerely,
123xiaoxiaode