Tigerlily, I take it this lady knows she is dying? There's no need to be maudlin or to mention her condition - and it doesn't need to be a long letter. Just tell her you've been thinking of her, and you want to thank her for the help she has given you. Tell her what is in your heart - and send her your love. You may well regret it if you don't. You're right. This is a journey she'll make alone, and she may be reflecting on her life rght now, so I think she'll really appreciate your letter. Don't leave it too late - do it.