Give my sister a special souvenir. 18 years old means my sister is a big girl. As a sister, you can send her a book written by a writer he likes. If there is a book signed for sale, you can ask the screenwriter to write "Happy birthday to your 18-year-old sister" on the title page, which is particularly memorable. I'm sure your sister will be very happy to receive this gift.

Or you can make a gift that your sister likes, knit a scarf for your sister, or make a handmade bag. Such a gift will also be particularly innovative.