If she is applying from Thailand and is Thai then this question does not apply to her. If, say, she was applying from the USA because she was there on a greed card then she would have to state that she had a green card.
Just put "Not Applicable - I am a Thai Citizen applying from Thailand".
If she is your girlfriend the UKBA may suspect that she is coming here to settle with you. You may consider going to a local solicitor to get them to draft a sponsorship declaration in which your state the terms of the visit (ie. just for a holiday), that she is to return at the end of it, that you both know that she must leave at the end of the visit because it would harm the chances of any future application made to secure leave to remain on the basis of that relationship, that you shall accommodate her and shall pay the costs of any unforeseen expenses that should occur during her stay so that nether of you will need to access public funds.
This should cost around £50+vat and you can find immigration solicitors via:-
She must also submit bank statements (etc) showing the monies she has available to her during her stay to show that she has sufficient funds to support herself during her stay. You can submit bank statments as well.
She has to also submit documentary evidence supporting the fact that she is to return to home. Things like a letter from her employer stating she has a job and is expected to return to continue that job, evidence of continuing accommodation (eg. tenancy agreement of evidence of ownership of a property).
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