I dont know what to do with our pitbull........i cant trust her?

ok so yesterday i had a horrible accident happen my brothers pit attacked my chihuahua and almost killed him we were all there and tried to stop him and my husband just couldnt get the stupid dog off my poor dog and the pit bit him and shook him then grabbed him with his mouth which covered his whole body pretty much and drug him under the house and my hub threw a rick at his head he stopped looked at him then went right bak to my dog!until he got under there and threw another rock!now im horrified of them becuase i saw how strong they really are and we have a female whos perfect with us and our children but doesnt like strangers like im sure she would bite if someone came in our yard becuase she already has growled at 2 people!!!but i dont think shed ever hurt us i dont know if i need to get rid of her or what to do shes my hubs and yesterday he was having 2nd thoughts of her like he didnt trust her.my chihuahuas fine though nothing broken just sore and started walkin today!=]