Unfortunately, it's actually very common for a brother or sister to have trouble sharing a toy sometimes. Since you are the older sister, this is a good opportunity for you to help your little sister learn about sharing. By setting a good example and sharing your toys, your sister will likely learn good behavior from you.
To begin, you might ask her to come and play with you and your toys. Perhaps there is a certain toy of yours she really enjoys. After doing this for a while, you might again ask if she could share her toys. Hopefully, by learning from your good example, your sister will understand that she should treat others the way she wants to be treated.
We hope this helps! Your parents might also have good ideas for you, too.
Art by: Keith Frawley