What are the requirements and best options for securing a DTV visa for training in Thailand?

I'm looking for advice for my daughter. She has been living in Phuket training on a swim scholarship since April, 2023. She needed to go home to get her passport renewed and is on her way back. Before she left Thailand, the training center told her she needed get a DTV to return. She flew to Laos and had the training center invitation letter and letter of support; however, she was denied as they said the letter of support was not enough and she had to have the 500,000 baht in her account. The training center continues to argue with us that they do not have to have the 500,000 baht. But we've had the same issues with Beijing embassy and Los Angeles (via email enquiries). We do not want to keep paying to fly her to different embassies and getting her DTV denied. She is currently coming back to Phuket on visa exempt (US passport) and then will try to find the best option for a longer term visa once she gets here. So my questions are:

1. Is the DTV the best visa for her to be on for training or is there a better option?

2. Is a letter of support from the training center enough?

3. If DTV is the best option, which country should I fly her to for that?

Thank you for any advice or recommendations you can give?