"Sully's Irish Banjo Book" by Anthony Sullivan (All Ireland Banjo Champion 1976) was/is a source of inspiration for me and also some great tunes.
As is the case with a lot of the "older" tutorial material, the 'basics' are covered sparsely but comprehensively. The expectation is that the pupil will learn and achieve each step before moving on to the next.
I don't have a fiddle background, but came to tenor banjo via guitar and whistle, so I had to learn to "read for banjo" ... your friend will have the advantage of being familiar with the music and having fretting-hand dexterity, just got to learn the picking hand

Good luck
