Can my wife convert her arrival into a Non-O visa after returning to Thailand?

she can convert the VISA EXEMPT entry stamp to a Non O

i did in Dec>

there is no arrival visa for western Passports

She was a silly Billy lol 😆

There's no difference between a tourist visa and visa exempt. They can both be converted to non-O inside Thailand. You must have 14-21 days remaining on the stay though so a Tourist visa gives more time to get things ready.

You did not tell us the reason for non-O though so it's difficult to give accurate advice. If you are planning on getting retirement extension and she will be trailing spouse without meeting the requirements on her own, this cannot be done in Thailand and she would need to wait until you're on the full 1 year extension then she should need to leave Thailand and apply for the non-O at a neighboring country.