S: it sounds like that you have been able to train a degree of impulse control, but after an amount of time, she feels no other way in relieving the pressure than to react, which of course ends the pressure as you remove her and the other dog is gone too.
The other thing to consider is that going through this drive process (the aggression) is chemically rewarding too so it can be reinforcing the behaviour so this will influence the dogs desire to react.
Sh: I agree with this. One thing I didn't mention in my initial post is that she has attacked my own dogs too. She attacked my old German Shephard 3 times (at ages between 12 - 15 ). The German Shephard was not an aggressive dog at all and would lay on the floor yelping while being attacked.