Does your friend have a bluetooth refreshable braille display?

You can read epub formatted ebooks through certain apps and the refreshable braille display *should* totally be able to handle that.

I believe it works for macOS & Windows as well. There's so many configurations that I can sometimes be a nightmare to get everything working together though.

I can't guarantee this will work, but my suggestion would be to attempt to just modify the file extension directly.

Both brf and brl can be opened and interpreted by a standard text editor like Notepad or Notepad++, so open it through notepad and then save as (making sure to set the save as type menu to "All Files"), and change the file extension from .brf to .brl

Make sure to get your friend to test a file first before converting all files. Hope that helps.