she will be able to use a PIN number until the ATM card expires. Then what? Just make a will making her the beneficiary of the account. It's so easy to do.
problem with the joint account is that you won't be able to use the banking app to pay for anything or to transfer money. Those banking rules came into effect a few years ago. Better to make a will which is a very simple thing to do here.
that's also the case with the Krungsri bank app. It won't accept a scan of the PEA QR code. But it works with Kasikorn which is my favorite bank. Also no problem with AIS prepay.
Krungsri Bank was very easy. I don't know about now though. I opened a Sterling FCD account with just my passport. Note that you have to fund the initial deposit with actual pound notes.
I can only speak of my own experience. I came into the country only on a Visa exemption. I then funded my account with 800k lump sum and then applied for a Non-O at Phuket immigration. Once the funds were seeded for 2 months I then went back to immigration and made the one-year extension based on retirement. I didn't have to leave the country to do it.
You have to leave the country to make a non-OA but not a non-O.
I was once given a 6-month extension right up until the last day of the expiry of the passport which had 6 months left when I applied for a one-year extension.