R.B.
just be with her! laugh with her, cry with her. offer rides to and from treatments (she will need them as she wont be able to drive after the treatments). on weekends go over and help with house work. take her daughter for a night or two so she can sleep. make some meals that all she will have to do is heat it up. make sure you respect her wishes and don't take offense to them.
my grandfather is going threw the same thing right now. he has cancer of the lung and lymph nodes. at times he wants to be alone (expectally after he lost all his hair that he was very proud of) then would get mad cause nobody was there when he didn't want to be alone. its an emotional ride for all involved trying to guess thier mood swings! he isn't too bad with just the radiation 5 days a week, but when he has to go in for the chemo shots he is wiped out and bearly wants to eat or do anything but sleep. one good thing he hasn't gotten sick once with the chemo shots.
good luck and she is lucky to have you as a friend. it may be draining on you and your family doing all the extra stuff for her but she will apprecate it so much in the end!