Who to ask about the update after a campus interview.
Most academic departments can't actually make hires for their university without higher university approval. This is because faculty hires are a long-term obligation for the university. Typically, it is a commitment of several years, at least until you get a third-year or tenure review. 

Therefore, the process is that the university allocates the department a "line" which means they have permission to search for a candidate. Then the department interviews and chooses candidates. The final step is for the university to formally offer the position. However, if the university's priorities or budget changes during the hiring process, the department can lose its "line." This happened to some U.S. state universities recently because state legislatures cut budgets and made hiring "freezes" necessary.

What seems to be happening in your case is that the department has chosen you but the university is dragging its feet on making the decision final. This is likely because they are not sure of their budget or some other aspect that is out of your control. It is possible that the chair can continue to push for your candidacy a bit harder (making the case that even if some departments lose their line, her department should not), but there is little that you can do about this situation. I would continue to look for other positions.

In terms of who to ask, stay in contact with the chair as best you can, stressing your continued interest in the position.