Just keep on caring for her the way you always have. Don't change a thing. Tell her nicely, that it hurts you that she wants to keep you at distance because of her illness, and that you will be there just as if she were perfectly healthy.
In the end, it will be tragic for you, but all caring and love seems to come with a price of pain to some extent.
She will feel cared for and loved, if her time here is over, and if she is to have time left here, your devotion to her, will be irreplaceable.
So sorry that this happened to you.
Beth