Weird. It's been a while since I joined. Can't see where it asks for a referrer though. If you go back and see where it does, but 'bifftastic' and see if that works
Visiting you would be the main reason. As with the first visa you applied for, you will need to show good reason to return every time she visits you. Strong ties to Thailand etc etc. Strong relationship with you. As I said, not dissimilar to the one you already got, but I believe they will be looking out for people who try to circumvent the settlement route by getting a longer length tourist visa (they're MUCH cheaper) so all your evidence or explanations will most likely need to be very strong.
Best bet is to jump on the Thailand-UK forum that I posted, as this thread will most likely be shut down soon (not Thai visa related), and that forum is where I got all the advice for our 6 previous UK visas from. Very good people on there.
It's a similar process to the 6 month application. You just have to show a good reason for regular visits. Also remember that a person who holds a two year tourist visa can not stay in the UK for longer than 6 months in one year.
If your partner wants to actually stay in the UK for two years, then she will need to apply for a spouse visa and complete the tests that go with that application.
In Thai it doesn't mention anything about transactions. It says ไม่น้อยกว่า ฿500,000 โดยต้องแสดงบัญชีเงินฝาก ย้อนหลัง 3 เดือน which means; No less than ฿500,000 must be shown over the previous three months.
I would suggest that that is the same as the other visa requirements where the amount required MUST NOT FALL BELOW the required amount during those three months. Usually referred to as 'seasoning'.
Quite why they mention transactions in the English text, I'm not sure.
Personally, seeing as it's a Thai visa, I'd prefer to rely on what it says in Thai rather than in English.