Proofreading courses are usually run by correspondence firms merely trying to cash in on another 'part time job' opportunity.
Originally, proofreaders were in integral part of a printing or publishing company. To qualify or 'graduate' it was usually necessary to serve a recognised apprenticeship. However, in these days of desk-top publishing, almost everyone thinks that proofreading is a simple matter of looking for spelling mistakes.
Far from it.
With the advent of desktop publishing, the traditional proofreader became a rare specimen. you will probably agree though, that language appreciation has taken a downhill path in recent years.
I wish your friend well, but a correspondence course is going to cost in the region of �300 - and will definitely not guarantee a source of proofreading work afterwards.
If interested, have a look at this website . . . .
www.perfectword-proofreading.co.uk
Best of luck.