Hello,My name is 谭心雨,Nice to meet you.you said that your friend copied your homework and falled the exam every time.As her(应该是女的吧？）friend,you should help her rather than make her more bad.First you should have a talk with your friend .Talking is a good way to solve problem .Don not worry about that you said things to your teacher,your friend will understand that you want to help her.your friend will say thank you to you after your friend understand that you want to help .so, don not be under pressure no longer!