I am in a panic! My sister recently came down with cancer and was a single mum. Now my niece is staying with me! It seems impossible she has cancer, she never seemed like she'd ever have something wrong with her. She was positive even when she got divorced. Now she's sad, I know it, and even though she tries to cover up, she's worrying too. How do I care for my niece?? She's 13 and very upset.