All those advices come from the perspective that she really IS an INTJ:
First of all, she ain’t slow. If you think so, you are either mistyping or misreading her. She actually thinks as good and as fast as you do (probably faster, statistically speaking). The thing is that she doesn’t need to talk so much and so loud about it, that’s all.
Also, good news: you can’t scare her by being an ENTJ. In fact your minds work pretty similarly and she will actually like your defectiveness and assertiveness. What you both SHOULD be worried about, specially you, is what I call the “J” conflict. Whenever your opinions differ, this should:
a- take to a long NT discussion that should make you both grow providing you are both equilibrated and your overall life views are not radically incompatible. Luckily none of you is likely to take it personally, but maybe you should state that out loud (if you are both correctly typed the moment you say 'I also like to discuss and understand the difference between disagreement and fight should be a moment of identification).
b- make her (specially if the relationship is not really solid yet and you don’t know yet how similar you really are) jump into (bad) conclusions about you without speaking her mind. This is obviously the BAD way to go about it. INTJs would do that if the thing does not affect them immediately, but over time, this could poison any relation (as they form a bad image of you). So, what I’m saying is: don’ let any intellectual rough edges, but be sensitive while addressing them.
Having finished about the intellectual part, we should go for feelings. You know when people think you are to cold and to objective? Good news, she’s exactly like you. If things go right, you should have a stable relationship with rare, but deep displays of feelings. Not that you won’t talk, you will, but most on the rational level. The feeling exchange that WILL happen, though should be intense to the point were both of you should remind to cope with it the other’s intensity and not be harsh about it, since you both hide and protect your feelings so much. Those moments should be respected.
Overall you’ve found a good match, one that I envy. Try to focus on the similarities and rationally polish the edges on the differences over time. Best of luck.