Radiation therapy and chemo nausea + vomiting seem to be treated the same way. Your friend should ask her oncologist to prescribe her an antiemetic. There’s a segment in this article on ANTIEMETICS .

I was prescribed Dexmethsone each morning for 2 days after treatment.

I was also prescribed metoclopramide hydrochloride pills to take whenever I felt nausea coming on after that.

This combination worked very well for me. I could not have got on top of the nausea and vomiting without them.

I also used the natural things like drinking lots of water, eating crystalline ginger, eating bland food with no strong aroma etc!
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3188425/
https://www.uspharmacist.com/article/management-of-radiationinduced-nausea-and-vomiting#:~:text=According%20to%20the%20ASCO%2C%20patients,antagonist%20(prochlorperazine%20or%20metoclopramide).