I'm not an expert, as my two have not had this battle - but it sounds to me as if there are two difference, but related issues going on.
Tia may well have matured and be challenging Archie for "top dog" position.......the fact that they are fighting suggests that Archie isn't prepared to defer to her without a fight
Alongside this, there may be resource guarding issue, that led to the bite that your daughter received fro Tia.......the problem is that if the dogs are fighting regularly, then Tia's adrenaline levels will be heightened most of the time and so she is more likely to be reactive to triggers and less likely to respond to training
Some dogs just don't get on; and even though they are different sexes, they are very close together in age, and so both may be competing for the dominant position
As I say, that it just my thoughts from reading your post.......but if you have not had any success with the techniques recommended by the behaviourist, have you been back to them? Sometimes, a technique won't suit a particular circumstance, and another can be tried with more success
