spontainious pitbull attacks on other dogs

Question
i have a 3 1/2 year old red nose and american mix pitbull, she a female, none spade. sometimes when me and me girlfriend are arguing the dogs seen nervious  they get ansiouty and sometimes will go off on each other when we argue. [their both females from same liter 1swt and last born of the litter] but me concern is for the last born her name is sissie. today we have been arguing more than normal lots of shouting  doors slamming ect...... i could see the nerviousness and sissie was, trembleing a bitthen i was told to leave the house so i gathered up some things, sissie was at the door waiting for me at this point,normally she goes with when i go some where she loves riding in the car and always at my side, so we proceeded out the door  without a leash , this is normal not to exit on a leash,she noticed a group of dogs being walked by their owners  just outside the door ,she attacks the largest of the dogs bitting on the dogs ear and  would not let go . this has happened before  same case sinario exsept on the other occations i yell at her or even grab her she stops . not this time, she would not let go at all fortchainetly  she lost grip and the other dog  got loose and i was able to restain sissie and put her in the vehicel  what the hell should i do .do i need to put her down or  is this normal under sercumstance. the other dog wasnt hurt badley  broke the skin , i had the owners take the dog to a vet to be looked at .the dog will be fine please help . sissie  is very loving, loyal ,never had a dog as friendly to other animals of all kinds including cats , birds ect..... this  seems to happen in spontainious situations, and when she is suprised  by the presents of other dogs as we leave our home

Answer
The situation in your home is causing your dogs a tremendous amount of stress.  What you saw in this attack is called "redirected aggression".  The "Pit Bull" is intended not to "let go" and this dog might be a clear and present danger to other dogs and perhaps even children when reacting with fear to what is going on in your home.

I suggest you get your dogs OUT OF THAT CIRCUMSTANCE and that means LEAVE THAT HOUSE and that relationship.  You will also need to have the dog evaluated by a professional (NOT a dog trainer).  She must be spayed but you must know she is not close to estrus before doing this (requires a blood test to measure estrogen levels).  A GOOD veterinarian might prescribe a beta blocker, propanolol, which short circuits the fight/flight response and allows you time to attempt to counter condition this dog.  You must find a Certified Applied Animal Behaviorist in your area from one of the following sites:
http://certifiedanimalbehaviorist.com/page6.html
http://www.animalbehavior.org/ABSAppliedBehavior/caab-directory

It is the CIRCUMSTANCE she is in that's causing this problem.  If the dog were out of control, a lot more damage would have been done to the other dog.  There's work to be done but this dog should not lose her life because of your problems at home.