Si is one trait that helps you memorize lots of variables. In ENFP, it's weak but in the preferred category -- i.e. if you exercise it, or see someone using it, it will make you feel better. Your ISTJ friend is probably exasperated by your failure to listen to what her Si has to say.
IJ types are actually less J than they seem and IP types are less P than they seem. ISTJ however is more S than they seem. J and S stereotypes overlap significantly, so probably that's what's getting to you. Si is very inflexible because the person does not want their physical world to undergo unnecessary change. They instead try to make life more comfortable and cozy. Ne types all crave this, because physical chaos distracts from their ability to make abstract observations.
If you're ENFJ that would make ISTJ your conflicting type. (ISTP would be your dual in that case.) But I think more likely this is a dual you're talking about -- you've been friends for a decade, and it sounds like they are criticizing areas you could benefit from improvement on anyway (and vice versa -- at least duality is symmetric). Out of curiosity, have your relationships with ISTP types been more positive or negative?