I forgot how she was in The Bad Beginning, but it could be that the circumstances have caused her to appear more extroverted as the series progressed. All of the children are forced to step far outside of their comfort zones in each book. I also think that she feels compelled to step in for her parents simply because she is the eldest, as well.
I can see INTJ to a certain extent. She is indeed reserved, with amazing focus that enables her to quickly sort through her ideas to find what is most useful. She also does seem to be more CtC than GtG and spends an equal amount of time implementing her ideas as she does contemplating them. With inferior Se, however, would an INTJ be so attentive to their environment? I can't really imagine it (being inferior Se) and what it's like, so I'm only guessing. Maybe it's that her development is speeding up because of the stress. Inferior Se would explain why she overlooks small details that Klaus can dive in to.
I hated the film version. The comedic factor made it more appealing to the targeted audience, but it ruined the series and Olaf's character for me. Blech.
I think Olaf seems more In Charge than CtC.
edit: Maybe Violet is INFJ. She does not possess the bluntness of Te and is always described as charming.