If she likes to eat, you can give her handmade blessing chocolates, which can not only satisfy her desire to eat, but also be very creative. You can engrave your blessing on the chocolate, which kills two birds with one stone. You can also give her some food she likes, such as the small snacks that are popular in snack shops now. She will like them.
She likes turtles, so you can buy her a few cute turtles. Turtle plush dolls are also very popular. You can give her a turtle doll. I think the best birthday gift for her is something she likes. The most popular gift in gift shops now is the crystal engraved piano music box, which is very beautiful. I believe your sister will like this gift too.
Maybe she will like Barbie dolls. My classmate is 20 years old and still likes that. Girls generally like Barbie dolls. In fact, the best gift for her is the one you carefully select. Whether it is food or something to use, your sister will like it.