Michelle,
I had a 6 cm tumor removed 18 years ago and was sick for years: nausea, vomiting, headaches, fatigue, the works. I was on steroids for 10 days and felt great but when they were discontinued, things started. I was told that steroids make you feel great and mask (not treat) any side effects one might otherwise feel. I don't think it is the lack of steroids that made Chelsea and I feel so bad, I think is is the size of the tumor. At 6 cm, the brainstem is very affected; mine was "compressed and rotated". Brainstem damage is known to cause nausea. Maybe, it is reacting to the need to return to a different position due to the fact that the tumor is removed. For Chelsea, it is possible that it is also reacting to the radiation treatments. How did she feel between the surgery and radiation?
Anyway, what helped me most is acupuncture, it made me feel great after every session. I had a series of 10 treatments every half a year or so and wish I had discovered it earlier. It might be worth a try for Chelsea. Try to choose a practitioner knowledgeable in herbs because there are quite a few that help. I tried ginseng when I was particularly exausted and my blood pressure was low and it worked wonders. In terms of other supplements, I am not sure what specifically helps but I would think that a poor diet and lack of vitamins and minerals would make you feel worse and delay healing and so would lack of sleep. I know how hard it is to eat healthy food when you are nauseous and vomiting. I hope this helps. I have been following Chelsea's story and admiring both hers and your courage!
Eve