Just cover the flight and daily life while staying over there
And you guys are not wife and husband
It’s harder than a wife and husband couple
Single Thai woman is hard to get the visa
The important thing that she could get the visa is tie to Thailand
She has to show the important reasons that she won’t overstay there illegally
She has to show many things that make sure she will go back Thailand before the visa expire
such as her good career, her debt that she still has to pay ( a house,a car) , doctor appointment that she has to come back , the family (parents,kids, pets that she must take care)
If the visa office trusts her by many documents that she will come back Thailand