You and your boyfriend's sister are classmates. She will be your relative in the future. You must remember her birthday, otherwise she will be sad. You need to think carefully before giving gifts to people with high taste in life. Let me give you some ideas.
1. Buy a pink 24K gold-plated rose for her. Such a gift can not only be used as a headdress, but also as a decoration at home. Women like flowers, let alone flowers that never wither. I believe she likes them more.
2. Handmade DIY chocolates with birthday wishes are a good choice for gifts. A box of such chocolates can not only represent your birthday wishes for her, but also satisfy everyone's taste.
3. Give her a set of cross embroidery sets. Girls love to do handicrafts. Such a gift can let her kill a lot of free time. Isn't it a meaningful thing for her to complete a work in her spare time?