Sweetheart don't be scared to give your mother the letter, I don't know your mom, but being a mother of a 12 year old girl, I can understand both sides, you mother will be hurting too when she reads your letter, she probably had no idea you were depressed or felt this way or were cutting yourself,(Teenagers are good at hiding things) she will want to reach out and help you, she loves you, remember that, even if initially she seems upset or mad, remember she LOVES YOU, and she will be there for you. Take care and I wish you well and that all works out for the best, good luck Dear.