no landlord will ask you for a visa; a month rent in advance and 2 months deposit is all they are interested. As for banks - you may need to see quite a few before one will give you a bank account. Immigration letter of residence is important but after that each bank is differently fussy; one branch rejected me as the lease pages were signed by just one person not both as on the lease. Other had a problem with surname being before the first name on the lease and the immigration letter. 3rd time lucky as the clerk wanted to finish for the day just before closing time. Easiest route is an agent, a 30 min job for any visa.
As long as she withdraws max amount of 30,000 baht the 220 baht fee is not much. Withdrawing 1000 baht being charged a fee of 220 however is extortionate at 22%. She will be able to get a local bank account once she has long term ED visa; Bangkok bank and Kasikorn easiest. Thai QR is absolutely essential.
Closing UK accounts would be a mistake unless the banks de-bank you. The 800,000 baht must be deposited on a Thai account to qualify for (first) annual visa extension.