Go on uk.gov website and look for visa requirements. Click her country of residence,obviously Thailand and it will tell you what sort of visa she needs, should be 6 month tourist visa. It will then tell you all you need to supply and it is quite a lot. 90 pounds may be the fee, I haven't done one for twin year's, but believe me, you will need to spend more. She will have to prove strong ties to Thailand to prove she will go home.
Will need home, job , bank account, family ties possibly, and proof of funds for her visit to the uk, you may have to be a sponsor and then you will also have to prove accommodation is available for her plus spending money,.
It's long winded and frankly pees me off when I see the hoops I had to jump through to get my girlfriend here then I see people just turn up on a boat and try to stay for life.
You can do it but believe me it's not like us just turn up in Thailand and being allowed in for 60 days with no visa at all.
It doesn't look like you have even completed or applied...if you had you would have a QR code sent to you so you can go and pay. Have you done that yet?