Dear Petunia,
I know we had our differences and I wanted to say I'm sorry for everything. You are my sister and you mean everything to me; you are family and I'm sorry for all the things I said to you and all the times I hurt you, all the times we fought and all the times I upset you.
I know that you don't want anything to do with us, with James or Harry or anybody, but even if I'm not here anymore you should know that they will be there in case you ever need them. You can count on them for anything you need, okay?
As my goodbye gift – I may not deserve a goodbye gift –, please give them a chance? Dudley and Harry can be cousins and James can go to your family reunions on Sundays… you can be a family together. I'm not saying they will forget about magic but it is not as crazy as it seems. I know you were jealous that you were not a witch but Tuney, you don't need to be a witch to be happy or live your dreams. You are living your life, the life you always wanted, and I admire you for it. I always admired you for your determination and passion and responsibility; I was never that.
Don't forget about me, Sis, I'm sorry for not being a good sister to you.
Love always,
Lily.