There are different kinds of vertigo. Some are related to damage from ototoxic medications, and the Epley maneuvers and medications don't do anything for this kind of vertigo. I have this kind of vertigo from a chemotherapy drug (along with tinnitus). Mine was very bad at the beginning, but has waned over time as I learned how to modify my lifestyle to avoid positional triggers. I highly recommend vestibular.org for self-education. There are some dietary things that have been helpful for me that I would recommend as a first step if your friend isn't already doing them. https://vestibular.org/underst...ment/vestibular-diet
I hope that helps.