thank you my friends for all this comments and advice. I already decided what I need to do and here is current development:
yesterday in school, during the class Jenny asked to go to the toilet so I asked to go to the toilet a few moments after she went. I went to womans toilet to confront her. I told her about what Harry said to me when he intiminated me and I told her she has a week until I blow the whistle on her and tell Carl myself.
at first she looked scared when I came in the toilet and towards the end of my speech to her she had tears in her eyes but didnt say a thing, she just stormed off beside me and got back to class. even though I understand and respect your advices and know what you talking about when you say things about her, but again I'm a dumbass because I felt sorry for her when I seen her with tears in eyes. I have known her for a long time and she helped me in the past also when I had hard time and I hate doing this to her but I think I have to. I dont know what she will do now but I think my speech got to her because she had tears in her eyes.
any further advice or maybe a hunch what can happen next?