My eldest sister went through Chemo after a double mastectomy, There are 4 siblings in our family, and to be honest, we all did different things to help. Chemo, as you know is a big thing, you feel ABSOLUTELY terrible, depending on the type of cancer and the drugs used for the chemo, tiredness, feeling nauseous, fingernails breaking off etc etc are all common. Initially I tried to make light of the situation, I had a huge pink afro wig that I gave my sister to wear when the hair falls out – that brought a laugh and helped lift her spirits a bit. You need to appreciate just how tired she will be, if she has kids, make sure they do more than just pull their weight, absolutely no arguments in the house etc. Also help by researching the type of cancer, know what questions to ask if you are going to the chemo appointment with her (she will unlikely be taking a clinical view to the proceedings so that task falls upon immediate family and close friends).
The need for support is huge, my mum moved in to do the housework, one of my other sisters ferried the kids to school, took care of the shopping etc.
External support (McMillan, Magie amongst others) are there also, not just for her, but for those supporting her through these tough times. They also offer good advice regarding clinical and financial support.
Above all, I would like to wish her all the luck in the world, if you want to have a chat, let me know.