it won't be easy finding a job though, being 60 or more. 60 is the forced retirement age for Thai teachers. That rule doesn't apply to foreign teachers, but, they are rarely interested in hiring someone over 60, unless you already have history with them, or offer to work for free or something.
As a foreigner, you need three things to legally work as a teacher in Thailand.
1. You need a visa that allows work (non B or non O based on kids/marriage as examples).
2. A work permit.
3. A teaching license.
You need as a minimum to hold a bachelor's degree, in any field.
You can transfer your existing license from California.
You would need notarized and legalized copies (and originals) of all documents, including diploma and transcript of your highest education and your teaching license if applicable.
you might be able to set up direct debit from a thai bank account/debit card. Never bothered with that. I just downloaded their app, in which you can see your plan, top up, pay bills directly in the app etc.
go visit a shop (ais, true, whatever). Not the random phone shop at the local market, but a brand shop. They can all do it.
I also have a post paid sim with true, started as a pre-paid, then switched. That was way before I had work permit etc. Only needed my passport as far as I remember.
Unlimited data for 299 per month. 5G full speed the first 25GB then throttled to lower speed. Still enough to stream video from Netflix etc without any cap.
if you trust her enough, you could give her power of attorney to the account. Without her name being listed on the bank book etc. Talk to your bank about that. But honestly, if you are just looking to make sure she will get it when.. Then being legally married is enough.