So sad

So today my pitty/boxer mix attacked my golden retriver 3 times. 4 grown men couldnt stop her. Thank god she quit but did bring blood. I have a 3 yr old so in the morning we are taking her to the shelter ): im so upset she is so sweet and has never shown agression to anyone dog or person before. But not willing to risk my baby so we must get rid of her. She was the first gift my husband bought when we were dating we have had her for four years. ):