As the saying goes, you rely on your parents at home and rely on your friends outside. When you go abroad, there are indeed many things that you can't handle by yourself. You are unfamiliar with the place and need someone to help you. With such a sister helping you, it must be twice the result with half the effort, and everything should be relatively smooth.
I think that the gift is not about the price. The important thing is to let her see your gratitude without being shy, so I suggest giving her a small gift, focusing on the feelings.
I recommend DIY chocolate. It is not necessary for couples to give chocolates. Express your gratitude and make your gratitude on chocolate.
Makeup mirror, a very delicate makeup mirror, girls all love beauty, this is also a very good gift.
There are many such small gifts, there must be what you want, you can choose to give it to her, I hope it will be helpful to you.