Your girlfriend is allowed to stay in the UK for 6 months if she gets the visa. Doing the visa application by yourself is definitely an option if you wish to save some money.
Can my Thai girlfriend come to the UK for a holiday?
Thai Girlfriend issued a Tourist Visa When a Thai girlfriend is issued a UK Tourist visa, she will only be able to travel to the UK and Northern Ireland. A UK tourist visa application made at the British embassy in Bangkok takes normally 5 working days to receive an outcome.
How long can a person from Thailand stay in the UK?
How long can a Thai national stay in the UK? You can stay in the UK for up to 6 months with a general visitors visa. And you may also apply for a long-term visit visa if you can prove you need to make repeat visits over a longer period.
Can my girlfriend move to the UK?
You need to be earning a certain amount, or have enough savings, in order to bring your partner to the UK to live. This is called meeting the financial requirement. You dont need to meet the financial requirement if you have refugee status or humanitarian protection.