Ne.and how they take in impressions.
(I probably have those switched backwards in another one of my sensotard moments. :o )
Maybe it's just my 4-ness talking, but I feel that INFPs have a strong sense of who they are that's not necessarily tied to just their values. I would try to connect to her on some level, either through a shared experience, a shared background, by noticing something about her that is unique (how she answered a question in class, how she is considerate of others, etc.) and mention how that made you notice her and that you'd like to get together for coffee or something similarly laid-back. That way, you're flattering her in a way that actually flatters her INFP-ness, is not trivial, and is more romantic without being too forward. Just my thoughts in a general sense; everyone's unique in their own way.