[mcg0106]

Hello,
I am studying abroad in Japan. Today, my class visited an all girls highschool & interacted with the students there. Each of us were assigned one girl in particular to introduce ourselves to and be guided by. Miku is 14 and a (third year, I believe) middle school student. I am a 19 year old college sophomore. I want to send her an email. I am wondering how I should address her. She is quite a bit younger than me, thus -san sounds slightly awkward to me. "-chan" seems more natural (given her age and manner) but seeing as we just met today, I don't want to sound overly familiar. Basically, my questions are: does -san sound too formal for such a young girl (addressed by myself, her elder) and if so, is -chan a suitable substitute?
Thanks,
Megan