I'm an Ovarian Cancer survivor...will be 6 years end of July. I can tell you I froze after each chemo tratment. At the same time I sweat buckets. I wrapped my self in a fleece blanket I had made prior to my surgery/chemo. It was very long, so I could tuck my feet in it & I put arms in it, so I wouldn't have to uncover to reach for anything. I also made it long enough to pull up over my face. Yep my face was cold too. I only had my eyes sticking out for a few days after each treatment. I would think anything you make her will be a grateful gift.
I would prewash & dry the flannel, as it shrinks a lot. You can layer it or add batting, what ever is not too heavy. Chemo causes bone pain & your skin can hurt too. When you have it al done I'd wash/dry it so any chemicals will be washed out prior to her using it.