20 years ago, QR codes were only twinkle in a developers eye and it's only in the last few years its taken off in Thailand. I can see a time when only bar girls, drug dealers and the like will use cash.
You already know she needs to convince the UK immigration that she will return to Thailand, she has a slim to get a visa without strong ties, in the comments someone mentioned Paul King his services are excellent, however, you must provide him the basic information and from you say it looks bleak.