INFPs can be overly modest & need to be hit over the head that someone is interested in them romantically. Sometimes they don't know how to respond when they realize someone actually is interested.
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Very accurate. I don’t assume anything or take anything for granted.
Between you & me & everyone else here

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you could probably exploit this aspect of INFPs. I'm pretty sure loads of INFPs end up with xSTJs because they doggedly pursue the INFP until she caves (more typical behavior of the xSTJ than xNTJ, IMO). You might not want to win someone over that way, but I think it's an option.... If she was really, really not interested in the tiniest bit, then I think that would be clear by now.
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LOL So true… my ESTJ pretty much sent me the equivalent of a memo letting me know we were now in a relationship. Whereas an INTJ had an opportunity to have something together for several years, then proceeded to profess undying love after I was already married. We are often so full of doubts about various aspects (the other person's feelings, how to act, what to say, etc.) that them taking leadership in the relationship is a very effective strategy. That’s why I said the way you asked her out was A-ok.
My personal experience with INTJs is just that... I'm curious about them, just enough to go out a few times, but if doesn't begin to develop beyond a curiosity (which it never has thus far), then I lose interest. You have to squeeze every ounce of potential & make it work for you, then you must make sure some of that potential begins to manifest as a real connection. Then you will have caught the elusive, ambiguous INFP

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Hmm. This might be an enneagram difference as well. I don’t need them to do cartwheels to establish a connection at all. I just need them to be their truest selves, and I need to understand very definitively in what ways I am set apart from others in their heart and lives.
Please also keep in mind that the INFP is neither an extrovert nor a Fe type, and that you're not going to get openly flirty & gushy typical girl behavior. Every single guy I've ever dated has said something like, "I can't tell how you feel about me" within the first few weeks to month or so of dating. I probably seem very ice-queenish at first...that's just how it is. I'm slow to warm, and it seems this is not unusual for INFPs. However, I see the contrast in myself with my usual behavior, and part of that is a willingness to make time/effort to see someone when I'd otherwise be content to not socialize.
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This is very accurate.
It would really help if we knew her enneagram type. I do wonder if the 9, 6 & 5 type INFPs are possibly more guarded romantically than the 4, who I think is possibly the most risk-taking in romance. 9s seem like they fall faster though (?), but they may be passive about rejecting someone too (?). As a 4, I'm novelty-driven enough to have a "let's see what happens" attitude, but then have too high ideals that will make me lose interest shortly thereafter. 6s seem the most anxious/suspicious about the unknown. I'll over-analyze, but it tends to be positive speculation, imaging ridiculously good things. I rarely see "disaster". It's either interesting enough or not, and if it's interesting, then I think about how it could meet some ideal.
I think enneagram makes a huge difference. As a 9, my beloved peace, equilibrium, stability, serenity, and security are paramount. I think 9s may be more discriminating and realistic for this reason, but once the subject is vetted, buy-in completely, as opposed to the 4 who might be more wishy washy, emotionally driven, and flighty in their interest.
Of course one’s instinctual stacking will also make a huge difference.