My mom went through chemo during a beautiful summer about 3 years ago and she loved the caps I made for her. She was always cold even on a hot day. So, chemo caps out of bamboo or cotton I'm sure would be much appreciated. Some chemo receivers also have the same problem most of us would - fear of being bald in public when you are not normally bald. My mom (and others going through chemo since then that I've made caps for) loved the lightweight of the caps and they made her feel better about her appearance. I can't tell you the number of compliments she received on them. The oncology center liked them so much that I made about 20 of them in all different colors and donated them. Apparently, they were all snatched up in a heartbeat. I'll definitely be doing that again!
Here is the pattern and yarn I used. It's soft and gorgeous. Definitely make the large size. Some of the yarns even look like hair (in taupes or brown or white).
All the best to your family friend. This fight is winnable!