A neighbour works off shore and his Thai wife is interested in doing a TEFL course and doing part-time speaking and listening classes in her house with high-school students. She’s pretty much fluent in terms of speaking and listening, but I don’t think she’s studied all the grammar side of things, and probably doesn’t know much about verbs and nouns etc.

I’ve no idea about it. Do TEFL courses take on Thais? Do they need to have a certain TOEIC score or whatever it is? Are there cheap (and nasty ) Thai run TEFL or teaching courses for Thais?

Not cheap, most will take students regardless of nationality if they are fluent speakers. Some of the lower tier run TEFL programs take everyone.

Typically though their primary focus is on communicative approach. Bilingual teachers have more assets and would limit themselves if they only did communicative approach.

Personally, I think it wouldn't be a wise investment of time and money for most Thais. Self study have her read books on the field.

How languages are learned by nina spada,

How to teach English by jeremy harmer (compilation nothing original but good overview of EFL teaching) 60-70% accurate for Thai classrooms.

Michael Swan's Practical English grammar

I am not near my library right now but she should also get some books on education theory focusing on task based learning which the new buzzword is student centered.