Dear Katy,
Hi! It was nice to receive a letter from you. I am doing great, thank you. Please, don't worry about me. How about you? How are you getting on at school? What about your parents? Tell them hello from me.
You were absolutely right - those friends were not so good as I thought they were. They were unreliable and impolite. But I was so happy to make some new friends. Now I know that it is better to think myself, not follow the other people's opinions.
Oh I shouldn't have skipped my classes at school too. I feel sorry about that. From now on, I will study harder and get only good marks.
Thanks for all your advice and support. You are really my best friend. I wish we will meet soon. Maybe you will come and visit me. My parents would be very glad to see you.
Yours sincerely,
Sarah.