Just keep reminding yourself you are working on this; that she is not your family and that it is all transference. I understand how you feel, my T was that age too and my mother died when I was very young and my stepmother died while I was in therapy, etc.

Go beyond looking at the dying part and look at why that would "matter" to you? My gut reaction was, "if she dies, who will take care of me?" because I lost my mother at such a young age. See what is actually driving your fear and tell your T and work hard on that.