she has to go Labour first, than take the paper I think TM10 to Immigration to cancel extension and yes, she will get fined for overstay. But that is the correct way.
not in Labour and Immigration records. Immigration record will just show that she left the country and "lost" her extension. Means if she not come back to Thailand no problem, if she come back and apply a new Non B that "unfinished" record will come back and haunt her.
show me picture of that visa. What agencies sale is , at least in Bangkok, a one year work permit tied to a Non O "Volunteer", but to maintain the Non O people are requested to apply a new Non O every three month, outside Thailand.