Actually with any kind of destination wedding, even if you invite people that does not mean that you have to pay for all or anything. There is no one set rule to follow. At our company we have seen some people pay for maybe three nights at the resort, or a set $200 per person or nothing at all. Another situation is that some see what it would have cost back home then the parents give some money towards family members traveling. But it is very rare that someone pays for all.
Basically when someone asks me this question I tell them that you don't have to do anything, but do what you feel comfortable with. If you want to pay for the whole thing, then go for it. If you want to pay for the airfare, then go for it. I would not pay for the meals except for the main group dining because that is a very personal nature that you don't want to go over and offend. Maybe the two of you can take her out for a breakfast, lunch or dinner outside of the group.
I know there is no magically answer just go with what you feel comfortable with. This is your wedding not anyone else.
Best Wishes on your special day!
Lindsay