Can my Mexican wife stay in Thailand under my Non-B visa as a dependent?

Okay, we got this sorted out, and there's not much more the O/P can really do other than take their mexican spouse to a thai consulate and BUY a real tourist visa OR bounce them out and back to get a new 15 day visa on arrival entry for 2000baht when they stamp back in

Your wife should get a non-O based on marriage with you (as non-B holder), and after three months the corresponding extension of stay. Your employer should arrange that.

She can be on Non-O dependent on your Non-B if your employer agrees to provide the necessary documents. It depends on her legal relationship with you, not her nationality.

She needs to apply for an actual pre-purchased visa at the Thai embassy or consulate in another country as she cannot do any directly from VOA entry. She may be able to get one of them:

- actual Tourist Visa to do in-country process if your employer can meet the requirements and provide necessary documents for in-country procedures for her

- Non-O dependent on your Non-B once you get Non-B, or at the same time with your Non-B application if your employer provides necessary documents

Required documents for her might vary by the location where she applies for her visa (Thai embassy or consulate in which country, or immigration office in which province). Check with your employer/school well enough in advance.