I'm deeply sorry for her! Sending love and healing light towards her. If you allow me, I could try to cast a healing spell for her.
What you and the coven want to do, seems right to me. I don't usually do anything more than healing spells and astral healing..so can't help much there.
I can recomend you/her some herbs allowed by doctors, but they don't always talk about them, because they can be replaced with synthetic supplements:
Before chemo sessions, she can take ginger and mint oils. They ease the adverse reactions to the chemo.
For the immune system, she can take medicinal shrooms (a nutritionist can write a prescription for those...and I won't say the name of the used shrooms here, in order not to give the younger members funny ideas)
Other herbs that can prevent and help in the process or curing it, are Curcuma, Garlic, Green Tea, Tomato pasta, Indian basil and Boswella.
Melatonin and Omega 3 supplements proved in studies that they can help the body resist to the medication better and keep the immune system up.
Lots of fruits and vegetables work miracles as well. She won't be able to eat many, especially if she starts chemo, but she can make juice out of the components of a fruit salad. She can also add raw potatoes, cabbage and carrots.
This is told to work miracles as well, but should only be taken after speaking to a nutritionist or a doctor, who can decide on the quantity. The chemical substance out of the bitter almonds and the pith of the apricots work like an alternative and less harmful version of chemo, but, same as the conventional remedy, if it's overdosed, it can turn into cianure in the stomach.
I will say those too, even though you probably already know about them. Qigong, Yoga, Massage, Meditation and Acupuncture also proved their efficiency especially after the conventional treatment, to strengthen the body.
"The strength of the pack is the wolf, and the strength of the wolf is the pack" - Rudyard Kippling ⛤