She is elder to you or younger?
Try to find out the reason.
She may want to play with you, or try to get your attention.
Some people do this they think that you got more love from your parents & she is neglected.
Think all things.
Then make her clear.
Try to be friendly with her & give her time be patient, soft, kind & always for giving. Your nice treatment will make a good human being inshallah.