When I was working in Thailand, this was the case in all the teaching jobs I had there. Some of which were in very reputable establishments. Unless she does something really silly during her 3 month probation period, she will get her WP. The problem is, what if immigration knock on the door? It is rare for this to happen, but has been happening more recently.
you come back on a 30-day tourist visa-exempt ticket. If you choose to get another job in Thailand you would have to leave again in order to get a non-Imm B visa to get a work permit. That's the way it was 3 years ago when I was working there. Don't get ripped off by agents.