I would get curious and see if I could tell when in her speaking I had the urge to interrupt, what the trigger is? I know when I read sometimes, I'll suddenly find myself in front of the refrigerator and when I backtrack I find there was a scary thought that was the impetus to suddenly be looking for something to eat. At one point, I actually put a book in my refrigerator to remind me what was going on.

I'd bring some item to therapy with me to hold, something unusual that makes me think about interrupting (condom? :-) or talking or an exchange (picture of a stoplight? stop sign?) and see if I could focus on my speaking, T speaking, my speaking, etc. and when that was hard and either T or I caught me interrupting, I'd instantly drop the interrupting and look at what was just said and how I felt about it, why I was trying to stop it.