Can my partner switch from a non-immigrant B visa to a tourist visa in Thailand after employment ends?

I worked in Thailand for many years until recently with a repeatedly renewed non-imm B visa, and was concerned about leaving work/Thailand properly so as to preserve the possibility of future visits. I informed my workplace of my intended resignation 30 days in advance, and my workplace did all the exit formalities/cancellations for me to leave work without my needing to go to any immigration office. I secretly wondered if my workplace had actually handled it properly, since I hadn't needed to do, or verify, anything in the process. I then left Thailand and spent some months traveling in India without returning to my native US, and came back from India to Bangkok as a tourist, hoping that coming again like this after my previous non-imm B would be all right. As it turned out, I received a visa-exempt entry for 60 days with no trouble, although I only actually stayed for three weeks before leaving again.

Should be okay but check with immigration and ensure the work permit and visa are cancelled. Follow what @john stanners is suggesting

It sounds sounds like would be applying for visa exempt not a tourist visa

Make sure your partner has already cancelled the work permit and Non-B visa.

Why go home. If she hasn’t been doing any prior boarder bounces in the last year she should be ok to do one when her visa ends. Make sure she closes out the Non-B and work permit. Just because she is leaving and letting them expire doesn’t mean she is fine with the process. I made that mistake once and it was a big hassle getting my expired visa closed.

I'm guessing she's actually on an extension of stay and not a visa, get her to check her passport. Assuming she is on an extension she needs to cancel her work permit and then take the documentation from that to immigration to cancel her extension of stay. She can do this a week or two in advance with a letter from her employer else she has to leave the day she cancels. She doesn't need to travel back home, she can just travel to a nearby country and either return visa exempt if entitled or apply for a tourist visa at the Thai consulate of whichever country she travels to

Yes this is Ok, if she leaves and comes in on a visa exemption for an holiday as a tourist.

If the immigration officer thinks she just trying to extend her time here they could refuse her.