How do I write........?

You'll have more luck asking the school to forward your e-mail to the teacher. Most schools won't give out personal information. In the e-mail you could say that the teacher was important in your education and would they please forward this to the teacher. If she wants to contact you she can. Include that you would like the school to let you know if they are not able to forward the e-mail so you know that you might need to keep looking.