Upvote:1
Easiest way if your GF shows that she has enough money for such a short trip, it is around one week. Just a reference from her bank account, showing that she possess and use her account regularly. I think having 2000 pounds for a several month on bank account would be enough for a 6 month visitor visa. Alternatively or additionally, a reference from her employer that she has a regular salary. Does not matter how high it is, it should be regular.