Behavior problems in 8 yr old

I’m worried about my daughter. She’s 8 and she has some serious anger issues. She is the sweetest smartest little thing and I’m an instant can go into a full blown rage. Tonight she kissed my pregnant belly. Got in bed told me she loved me and then asked for water. I brought her a cup she didn’t want and she flew off the handle. And then after about 5 crazy minutes of screaming and craziness she starts crying and saying sorry. She has 3 sisters and they don’t ever act like this. Any advice?