@Harrys ***********
Home Office might worry thst a low paying teaching job in Thailand isn't enough reason for her to return home. Her parent's might well be dead given her age. The bar girls aren't looking a holiday fling. Stick in an application now. It's going to cost you £120 or so to find out, unless she wants to use an agent. Agents can ensure that she doesn't make a mistake in the application, and can advise on the invitation letter. You need 6 month bank receipts, proof of accommodation, such as mortgage statement, deeds, lease agreement. I also provided salary slip.