sponsorship for like food and accommodation while in the US,tour packages will be handled by boyfriend who is a US citizen. A lot of paper work but the more proof on both sides that the intention will just be a holiday will be a big chance for them to get approve. Any advice that might help him would be great but he will still be the one who will decide👍🏼😊
It never hurts to try again until you succeed. The consul will tell your girlfriend why they are rejected. And there is a certain time to apply again for tourist visa after rejection too but not sure how long.Prepare documents like proof that she will be back to her home country, proof of funds, you can provide your medical records as well for her application or you can sponsor her trip but make sure that she we will be back to Thailand and the main purpose for US trip is only for holiday,Hope this helps you in a little way,best of luck.