How was the chemo given, orally or intravenously? Our dog was on an oral form of chemo and fortunately handled it pretty well. However, my best advice would be for your friend to contact their vet or oncology specialist, i.e. whomever administered the chemo treatment, to discuss the side effects. Sending my best wishes for your friend's pup.
My dog had both radiation and oral chemo for cancer of the urethra. For nausea they can give cerenia. We used Propectin to help with diarrhea. It is a probiotic that has kaolin in it to help bind the stool. My dog was on these chewables daily.
Have your friend call the oncologist and ask for help.