Depends on what she likes, does she like painting or going to the park? For me i gave in to what my baby brothers needs and wants, and when he got older i got a little more strict in giving in. It just depends on the kid, ask her what she wants to do, if not give her a few options of what you might think she'll like to do.
Not every set of siblings ie sisters get along. No two people are alike. You'll find this all through your lifetime. The best you can do is be nice, civil, and helpful when you can. Give her some time to grow up and some space for both of you and don't force your friendship on her or anyone else. Never works.