No, you should be fine. The guidance around her coming for a visit first is largely based around getting to know each other better and ensuring she would be happy here in the UK, but if you've been together for two years and lived together in Thailand, then at least half of that is a moot point.
In terms of income, you should be fine. £2,500 net is about £30k+ per year, gross. As far as I'm aware, going into overdraft now and again isn't an issue, you either meet the income criteria, or you don't. In terms of the mechanics, take a look at Frogster's guide.