I think that this is a successful letter. You're understanding of the fact that it must be hard for her, but asking her if she would at least be willing to try. You're giving her the space to make mistakes without judging her and being really kind with her. However, at the same time I think you've gotten through how important this is for you. I think it's successful. I can't think of anything that you should add or take away. To the point yet gentle.