I have a friend that I've known for quite a while, and we've always been very close. She and I both tested as INFPs but the more I think about it, the less I see it. I've been thinking that she could possibly be an ISFP instead. She definitely uses Fi as her main cognitive function, it's kind of what we bonded over. However, while she's always been quirky and odd, she's also pretty balanced socially. She tends to be more realistic, and for the most part keeps quiet in situations, even when she finds them distasteful. She waits until issues boil over to say something about it, but usually lets things slide. As an INFP, I'm constantly finding myself ranting about whatever I possibly can, and I have a really really hard time just "dealing with it". She and I also have creative differences. While I constantly put out odd, undeveloped ideas and abandon them pretty quickly, she tends to take inspiration from shows/books she likes, and sits on ideas for long periods though she rarely does anything with them. Maybe it's a difference in ennegram, or maybe she just got mistyped.
ANYWAYS my point is, can anyone give me some pointers on identifying the differences between ISFPs and INFPs?