How do I support her

We have recently found out that My Auntie, my mums twin sister has terminal cancer.  She has beaten breast cancer twice but this time it's back and there is little doctors can do but try to prolong her life.  My mum is taking it really hard and I am not sure how I can support her.  She knows I am there for her but I feel useless both to my Auntie and my mum.