my boxer is aggressive with other dogs

Question
I have a 3 year old neutered female boxer. About 3 months ago she started a fight with my mom's Australian Shepard, who she grew up with and lived.  They are not together anymore after the fight. However, my roommate just got a German Shepard pup and I am afraid that she might attack the puppy. Do you think I should buy a muzzle and try and train her that way? I just don't want to see her hurt another dog. Yesterday was there first meeting and Zoey, my boxer, growled at the pup and tried to go after the pups ear. This behavior is just so odd to me because she loves people and she is the sweetest dog. I use to take her to the dog park all the time and there were never any problems up until the  attack. Please help me!!
Thanks,
Jamie

Answer
Usually the best way to break this habit is to use a muzzle on both dogs and then sometimes they will sort out there order,and be done with it,and sometimes they will also learn that other dogs aren't going to hurt them

So it might be good to bring your dog over to your mom's and muzzle both dogs,and see what happens and that for a while,as you don't want to muzzle a puppy that is under 6 months,but if the boxer goes after the puppy right now only muzzle her