Well, I am not aware how easy or difficult to get a visitor visa from Singapore or Australia. I don't think it will be too difficult if we are well prepared. If it is really difficult; then she can apply a visa from Nepal. You don't have to be a US citizen to sponsor. Any one on legal status can sponsor a visitor provided that the sponsor is financially secured. A visitor gets a multiple entry visa that is good for 5 yrs. but s/he can stay in US up to 6 months without any problem. It is not too difficult to extend another 6 months of stay which means your gf can stay with you upto 12 months each visit. Then she will have to leave US for a while before she can re-enter for another 6 months. I don't know what your current visa status is. If you are on a non-tourist visa and on a good legal status, you should be able to petition her for a dependent visa if you guys get married. I hope these info will help you. Take care