Tell her she should go for it! She'd pick stuff up - they probably play many of the same songs week after week.
The local "bluegrass" jam here (they also play other music) is a blast - I go every Friday. I was completely lost at first as I'd never even played chords without music, but it has been one of the best learning experiences EVER. Most stuff is only three or four chords, so worst case scenario is that I play those or play the main note of the chord (i.e. D if it's a D chord).