Martin.
I don't know if your Zhifang has been married before, but if she has, then i can quite understand her parents sentiments. They probably received a marriage RE from her previous husband and would have been happy to receive it from him. Now, they are only interested Zhifang's future happiness, they are happy that she is happy with you, and that's more than payment enough for them.
I can't really understand why some parents would want or expect a RE when there daughters has been previously married, probably over 30, and probably with children. They know full well that the chances of there daughters ever finding a Chinese husband are slim to non-existent. Like Zhifang's parents, they should be happy that they have found a man that they can see with there own eyes, ....makes there daughter ''Happy''!!!
Giving gifts is a totally different kettle of fish, Give her parents a special gift(s). It doesn't have to be too expensive, just something that they will want, or need, or just special to them. Now that, ...they will appreciate more than any RE....
David.....