HELP please! Friend troubles!?

Ok so here is the story. My friend Lena has been extremely rude lately. Probably because over the summer, I let my friend Mary talk to Lena on the computer. Mary pretended to be me saying "Do you think Mary is annoying?" And then there was this whole conversation going on and I didn't even know! So I guess Mary said some mean things, pretending to be me. I finally figured out what she said when I looked at my chat history. Over the summer Lena sent me a ton of emails saying what I did was mean. I told her that it wasn't my fault and that Mary said those things I apologized a gazillion times and told her it wasnt me. She won't forgive me and she is just bein a total beeatch about it! At school, she is being super mean to me. She rolls her eyes at me, says everything I do is stupid (She was like "You played volleyball with a bouncy ball? That is so retarded." and then "What are you doing? God you are CLUELESS!") And she is super nice to everyone else INCLUDING MARY! She is a total meanie to me! The teacher told us to grade each others essays and when Lena graded mine she wrote "Its ok. Do better next time" when she had at least a million mistakes on hers! She is just being so mean and rude! So I need something to say to her. Something clever to make her know that she is being to judgemental and mean and rude and that she is making a huge deal and that she should just forgive me CUZ I DIDNT DO ANYTHING WRONG! Please help it would mean sooo much thanks guys <3