Aggressive female Jack Russell Terrier

Question
I have a 3 year old female Jack Russell.  She's very loving to those she's familier with.  My son recently got a male Chocolate Lab pup. It took a week or two, but they get along great.  We recently moved to a home with a 2-1/2 year old female bull terrier (the lab didn't make the move, just the Jack Russell).  The Bull Terrier has a sweet disposition, but the two terriers clearly don't care for one another.  The Jack will let out a low growl and then the fight's on.  Neither have been injured, but there are teeth showing and serious growling.  I did put them both on leash and walked them together today without incident.  I hate to think that they'll have to be constantly separated and certainly at this point would not leave them together while no one was home.  Today was the first full day they've spent in the home together.  Any suggestions to help make this work?  We're very attached to both dogs.  Thanks.

Answer
Two females who develop a fight on sight problem are quite difficult to rehabilitate and it certainly can't be done without evaluating both dogs in person.  This is a tricky situation and there are no quick fixes; both breeds are tenacious and dominant, high energy dogs; disposition toward humans does not predict dog to dog aggression.  What happened to the Lab?? This sudden disruption of the JRTs life is quite traumatic for her; so far, only one day has passed.  She is going to require some time to adjust to her new home, the disappearance of her pack mate, and the change in human cohabitants.  These dogs should have been introduced outdoors on neutral territory.  You can continue walking them parallel and attempt to use a play training object to redirect any aggression or over excitement, but you need a professional to evaluate this situation in person.  Don't leave them alone together and don't give them any opportunity to advance in their aggression toward one another, whether it be prompted by territoriality or fear.  Your best bet is to find a certified applied animal behaviorist by calling high end veterinary hospitals or the veterinary college in your geographical area.  Without seeing body language and interacting with both dogs independent of each other, it's impossible to make an informed opinion.