I think you do need to be careful because there are certainly scams that are built on this. You could try to build a relationship that's not just sexual. see how she is just talking general shit - still enjoy the sex if it's on offer, lol. Sex is always a good lure of course. the one i spoke with also wanted me to visit and in fact, to marry her. she seemed genuine and was able to chat about stuff other than just sex. also maybe test her patience. if she is still there in 6 months maybe there is more chance she is genuine. the girl i knew would often call me out of the blue just to say hi, even 12 months after we first met. i don't think you can ever truly prove their motives without actually meeting them though so i guess it comes down to how trusting you are.