I don’t know if it had changed or not but I did this 12 years ago took 2 attempts

I was refused the first time by someone who I found out later was refusing every application

I did all the paperwork myself it’s very important to have proof that you have been together for a considerable time

Photos with dates on

E mails printed out

Proof of phone calls

Places that you have been together

Also proof that she has a reason to return to Thailand family or a business

Also proof that she can support herself in the Uk photo copy her bank book make sure there is more than enough funds to support her stay in Uk

Also book return air tickets but be careful if you are refused then have to apply again this takes time so book well ahead or have tickets that you can change if needs be

Also a letter of reference or good character

Also your bank account details proving that you have a decent amount of money

Photo copy and print everything the more the better

Then put it in a folder and make a appointment to apply for visa we had to go to Bangkok

All the best of luck hope hope everything goes well for you

From United Kingdom you can get a single entry or a double entry which is a multi entry unless this has changed

If you get a double entry that means 60 days on arrival then go to immigration extend for 30 days that’s 90 days after that leave Thailand and re enter same process 60 days on arrival then extend another 30 in immigration total 180 days