AGGRESSIVE

My 3. dog is a 2 1/2 year old Boxer/Rottweiler mix name Lola. She looks like a Pittbull but is the sweetest girl in the world. She listens to me and loves almost everybody, especially children and other little dogs. I usually take my 3 dogs to the dogbeach every other day but I really feel the need to leave Lola at home lately. She gets so excited that I almost lose control over her. My sweet girl turns into a lion and starts attacking her "sister". I know that she plays cause they do that also in the back yard and since they were puppies. It's just that other people and dogs get totally alert by the sounds she makes. She looks a little scary and when I try to tell people that she is a very nice girl and they just play, they look at me like I'm crazy. Lola plays so hard and so much (I throw the ball) that she even limps the next day. And almost during all this time these scary sounding barks along with the attacks on her sister. How can I prevent her from doing that??? I'm scared that they will not let me take her to the beach anymore...
Please help!!!