"A sister is a piece of childhood that can never be replaced." " A sister is someone who genuinely cares about you. You cannot be drawn apart, no matter how much you dispute. She is a source of delight that cannot be taken away. You must remember these things when writing your sister a letter." So go on and let her know how special she is to you. Tell her how much you appreciate everything she has done for you. Remind her that you are always here for her, if she needs anything at all. Just keep it short and sweet, because there aren't many letters left now!