In China, seniority is still a very important culture, so all kinds of strange phenomena will appear. Many people call children uncle or something. But for today's young people, such things are just a little unexpected and funny. They are all of the same generation, and there is no generation difference.
For a birthday like this, if you want to give her a gift, you can give her a gift as a brother. Don't make it so formal. At this age, she will not like those etiquettes very much. So it is recommended to give a fashionable gift, such as a new MP3, or a pair of very cute small speakers. There are those DIY portable personalized speakers, which are very interesting.
Recommended name necklaces, makeup mirrors, blessing chocolates, cartoon bouquets, all of which are creative gifts. There are all kinds of, and other gifts, I hope it will be helpful to you.