Start with How are You? And listen for the answer. She may be ok physically, not mentally. Her body may feel ok...but her soul may be in turmoil. Ask her what she needs. Sometimes it is a friend to talk with, a meal (or two) so that she can eat. (Please be aware that some people can't eat certain things during chemo. I became violently sick with chicken...the sight and smell caused violent vomiting. But my doctor permitted me to eat salad and sushi..which is usually banned. My body craved both.)
In general talking is a good thing: about the news, future plans, politics, fashion, children. Whatever makes her feel normal and optimistic for the future. And sometimes, sharing a cup of tea (should you be able to visit) and silence is comforting.