I got a friend problem she is 10 yrs old and i am 13 yrs old how should i act around her?

okay she like keeps saying like "i can swim better that you then oh i was just kidding" and stuff and once near the 11ft diving part she pushed me and got in trouble and she is mad at me?? anyways how should i act around her or what should i do as an older person so that she stops doing these stuff or saying these stuff??? cause she never listens to me!!! and i want to be friendly and i want her to listen to me!!! and her sisters one 8 yrs old one 9 yrs old one 10 yrs old.......and she makes fun of people which she doesnt have the authoroty to do that!!!!!! and when ever i blob my head under water and come up she imitates me and exagerates and laughs at it !!!!!!!