Hi Faithful Witness, It is an awesome letter.
I would remove the sentence " Maybe some day you will be able to see things from my perspective." until after your relationship improves with her and you say it to her instead of writing it to her. JWs' cult personas are narsistic so your perspective is not important to it. Also, you do not know if your sister's authentic or cult persona will be reading the note.
Keep your note simple, send lots of pictures of you and your family having lots of fun, invite her to future outings, and tell her how much you love her unconditionally.
Peace be with you and everyone, who you love,
Robert