There are people there who post up actual lists of the documents they submitted and the results etc. and I both took advice and contributed when I was in a similar position. No need for parasitic agents.
The gust of the posts so far is true, that they need to be sure she will return. If she does not have a job with salary and bank statements then what about any record of your sustaining her and just how did she earn money.
It isn't that hard to get it put together but get someone to read it through and try to form an objective opinion.
If you get refused, you used to get some idea of why you were refused and you could address that in a subsequent application.
But the main things are straightforward, assuming she doesn't qualify in her own right on income grounds to fund her holiday. Family, job, will job be available if she is away for a period of time, property in Thailand, etc.
As for you, your finances aside, it is how long you have known her, communication, support, etc. again, not rocket science.
2 years ? Show me where that pearl of wisdom is in the law ?
The truth is that if you are weak then she needs to be stronger and the best scenario is if she doesn't need your sponsorship to go to the UK for a holiday.