I think it's Te. I am ISFP.. We have Te but it's something valued in others rather than something we first approach the world with ourselves. And vice versa with Fi for TJs. Both mirror each other and share the same primary functions, just in reverse. But I think she's ENTJ actually (still strong Se), while the Te makes her seem less extroverted than EPs. And she's a lot more future oriented and open (Ni) than STJs like Aveline and Cullen. My 2c.
You could be right and she's ISFP, but fully realized in all functions.. but that's apparently something that comes in old age and having your dual rub off on you. I'm not there myself. 
Similar to my mbti type! The internet is crowded with Intx types, i've never seen anyone who is an Isfp until now
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That is true - Te is a weakness for the Infp and Isfp types, so as an Isfp she would have to have a really good use of Te. She is orientated to the future and demands answers from people in fear of what could happen next. Inferior Ne types worry about future possibilities too, and I get the sense that xSxP types dislike uncertainty. I agree that she is different from someone like Cullen (haven't played enough of DAII to know what aveline is like). She is a good example of sensor - they are said to be grounded and good at making ideas a reality (as opposed to intuitive who are better with generating ideas and seeing future possibilities) . I found a description for Se from sociotype.com;
"The individual feels at home among people who are actively doing something and interacting with each other directly (visibly), and is able to organize people, move them around as necessary, and guide them in achieving a specific goal. He or she likes obedience and even subservience in others, since it allows him to "make things happen" more effectively. He is keenly aware of territorial conflicts and confrontational behavior occurring around him. He very quickly becomes confrontational when others try to make him move or get him to do something in an aggressive or confrontational way. He quickly recognizes when people are trying to get each other to do something or are trying to organize him for some purpose. He also spontaneously uses aggression to achieve his own goals. "
I think that describes her personality quite well. Perhaps it is Fi-Se in action that looks like Te. Because I also think she shows too much Fi judgement for an ExTJ type, compared so someone like Vivienne who has a different vibe from her. I think she could be a well balanced SFP or possibly ENTJ. She is a fictional character after all, so no type is going to make perfect sense for any of them.